Government Money Market Portfolio
SUMMARY PROSPECTUS
MAY 1, 2026
 
Before you invest, you may want to review the Portfolio’s prospectus, which contains more information about the Portfolio and its risks. You can find the Portfolio’s prospectus, reports to shareholders, and other information about the Portfolio online at www.nmseriesfund.com. You can also get this information at no cost by calling (866) 910-1232 or by sending an e-mail request to sfprospectus@northwesternmutual.com. The current prospectus and statement of additional information, each dated May 1, 2026, along with the Portfolio’s most recent annual report dated December 31, 2025, are incorporated by reference into this Summary Prospectus. The Portfolio’s statement of additional information and annual report may be obtained, free of charge, in the same manner as the prospectus.
The Securities and Exchange Commission has not approved or disapproved these securities or passed upon the adequacy of this prospectus. Any representation to the contrary is a criminal offense.
INVESTMENT OBJECTIVE
The investment objective of the Portfolio is to realize maximum current income to the extent consistent with liquidity and stability of capital.
FEES AND EXPENSES OF THE PORTFOLIO
The table below describes the fees and expenses that you may pay when you buy, hold, and sell interests in a separate account that invests in shares of the Portfolio as a result of your purchase of a variable annuity contract or variable life insurance policy. The fees and expenses shown in the table and Example do not reflect fees and expenses separately charged by variable annuity contracts or variable life insurance policies. If the fees and expenses separately charged by variable annuity contracts and variable life insurance policies were included, the fees and expenses shown in the table and the Example would be higher.
 
Shareholder Fees
(fees paid directly from your investment)
N/A
 
Annual Portfolio Operating Expenses
(expenses that you pay each year as a percentage
of the value of your investment)
 
Management Fee
0.30%
Distribution and Service (12b-1) Fees
None
Other Expenses
0.03%
Total Annual Portfolio Operating Expenses
0.33%
Example
This Example is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 
1 Year
3 Years
5 Years
10 Years
$34
$106
$185
$418
PRINCIPAL INVESTMENT STRATEGIES
As a government money market portfolio, the Portfolio invests at least 99.5% of its total assets in cash, U.S. Treasury bills, notes and other obligations issued or guaranteed as to principal and interest by the U.S. Government, its agencies or instrumentalities, and repurchase agreements secured by such obligations or cash. The Portfolio may invest 100% of its total assets in such repurchase agreements. Under normal circumstances, the Portfolio will invest at least 80% of net assets in obligations issued or guaranteed as to principal and interest by the U.S. Government, its agencies or instrumentalities, and repurchase agreements secured by such obligations. The Portfolio invests in a portfolio of securities maturing in 397 days or less (with certain exceptions) that will have a dollar-weighted average maturity of 60 days or less and a dollar-weighted average life of 120 days or less. The Portfolio may invest in variable and floating rate instruments, and transact in securities on a when-issued, delayed delivery or forward commitment basis. The Portfolio seeks to maintain a net asset value of $1.00 per share.
PRINCIPAL RISKS
The main risks of investing in this Portfolio are identified below.
•
Active Management Risk – The securities selected for the Portfolio may underperform the markets, relevant indices, or securities selected by other funds with similar investment objectives and investment strategies.
•
Credit Risk – The Portfolio could lose money if the issuer or guarantor of a fixed income security or the counterparty to a repurchase agreement is unwilling or unable to meet its financial obligations. In addition, changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Portfolio’s investment in that issuer. Changes in credit spreads or improvements in an issuer’s credit quality may increase the risk that an issuer calls outstanding securities prior to their maturity.
•
Income Risk – The risk that the Portfolio’s yield will vary as short-term securities in its portfolio mature and the proceeds are reinvested in securities with different interest rates.
•
Interest Rate Risk – Prices of fixed income instruments generally rise and fall in response to changes in market interest rates. In
NMSF-SP1Northwestern Mutual Series Fund, Inc.
Government Money Market Portfolio – Summary
a rising interest rate environment, the value of the Portfolio’s fixed income investments is likely to decline. A low or negative interest rate environment poses additional risks to the Portfolio. Low yields on the Portfolio’s holdings may have an adverse impact on the Portfolio’s ability to provide a positive yield to its shareholders or pay expenses out of Portfolio assets. Additionally, securities issued or guaranteed by the U.S. government, its agencies and instrumentalities have historically involved little risk of loss of principal if held to maturity. However, due to fluctuations in interest rates, the market value of such securities may vary during the period you are invested in the Portfolio. For example, the market value of a fixed income portfolio with an average duration of five years generally would be expected to fall approximately 5% if interest rates rose by one percentage point. Declining interest rates may increase the risk that an issuer calls outstanding securities prior to their maturity.
•
Liquidity Risk – Investments for the Portfolio may be difficult to purchase or sell at an advantageous time or price, if at all. These risks may be magnified during periods of economic turmoil or in an extended economic downturn.  The liquidity requirements applicable to government money market funds are designed to help mitigate the potential impact of these risks.
•
Market Risk – The risk that the market price of securities owned by the Portfolio may go up or down, sometimes rapidly or unpredictably. The value of a security may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Global economies and financial markets are increasingly interconnected, which magnifies the potential that conditions in one country or region might adversely impact issuers in, or foreign exchange rates with, a different country or region. Geopolitical and other events, including war, terrorism, economic uncertainty, trade disputes, tariffs, public health crises (such as epidemics and pandemics), and related events have led, and in the future may lead, to increased market volatility, which may disrupt U.S. and world economies and markets and may have significant adverse direct or indirect effects on the Portfolio and its investments.
•
Repurchase Agreements Risk – If the other party to a repurchase agreement defaults on its obligation under the agreement, the Portfolio may suffer delays and incur costs or lose money in exercising its rights under the agreement. These risks may be heightened if the other party is located outside of the U.S. If the seller fails to repurchase the security and the market value of the security declines, the Portfolio may lose money.
•
Stable Net Asset Value Risk – The Portfolio may not be able to maintain a stable net asset value (“NAV”) of $1.00 per share at all times. If the Portfolio fails to maintain a stable NAV (or there is a perceived threat of such failure), the Portfolio, along with other money market funds, could be subject to increased redemption activity.
•
Underlying Portfolio Risk – The Portfolio may serve as an investment option, or “Underlying Portfolio,” for other portfolios of Northwestern Mutual Series Fund, Inc. that are managed as “fund of funds.” As a result, from time to time, the Portfolio may experience relatively large investments or redemptions from those other portfolios and could be required to invest cash or sell securities at a time when it is not advantageous to do so.
•
Treasury Obligations Risk – Direct obligations of the U.S. Treasury have historically involved little risk of loss of principal if held to maturity. However, due to fluctuations in interest rates, the market value of such securities may vary during the period shareholders own shares of the Fund. In addition, notwithstanding that U.S. Treasury obligations are backed by the full faith and credit of the United States, circumstances could arise that could prevent the timely payment of interest of principal, such as reaching the legislative “debt ceiling.” Such non-payment could result in losses to the Fund and substantial negative consequences for the U.S. economy and the global financial system.
•
U.S. Government Obligations Risk – Certain securities in which the Fund may invest, including securities issued by certain U.S. Government agencies and U.S. Government sponsored enterprises, are not guaranteed by the U.S. Government or supported by the full faith and credit of the United States. In addition, circumstances could arise that could prevent the timely payment of interest or principal on U.S. Government obligations, such as reaching the legislative “debt ceiling.” Such non- payment could result in losses to the Fund and substantial negative consequences for the U.S. economy and the global financial system.
•
Variable and Floating Rate Instrument Risk – Variable and floating rate securities provide for a periodic adjustment in the interest rate paid on the obligations. The absence of an active market for these securities could make it difficult for the Portfolio to dispose of them if the issuer defaults.
•
When-Issued and Delayed Delivery Transactions Risk – When issued and delayed delivery securities involve the risk that the security will lose value prior to its delivery. There is also the risk that the security will not be issued or that the other party to the transaction will not meet its obligation. If this occurs, the Portfolio loses both the investment opportunity for the assets it set aside to pay for the security and any gain the security’s price.
You could lose money by investing in the Government Money Market Portfolio.Although the Portfolio seeks to preserve the value of your investment at $1.00 per share, it cannot guarantee it will do so. An investment in the Portfolio is not a bank account and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. The Portfolio’s sponsor has no legal obligation to reimburse the Portfolio for losses and you should not expect that the sponsor will provide financial support to the Portfolio at any time, including during periods of market stress.
NMSF-SP2Northwestern Mutual Series Fund, Inc. Prospectus
Government Money Market Portfolio – Summary
PERFORMANCE
The following bar chart illustrates the risks of investing in the Portfolio by showing how the performance of the Portfolio has varied from year to year. The table to the right of the bar chart shows the Portfolio’s average annual total return over certain time periods. Returns are based on past results and are not an indication of future performance. Prior to May 1, 2016, the Portfolio operated as a prime money market fund and invested in certain types of securities that the Portfolio is no longer permitted to hold. Consequently, the performance information below may have been different if the current investment limitations had been in effect during the period prior to the Portfolio’s conversion to a government money market fund. Neither the bar chart nor the table reflects the fees and expenses separately charged by the variable annuity contract or variable life insurance policy separate account that invests in the Portfolio and returns would be lower if those fees and expenses were reflected.
  
 
Quarter/Year
Return
Best Quarter
4th quarter, 2023
1.30%
Worst Quarter
1st quarter, 2022
0.00%
Average Annual Total Return
(for periods ended December 31, 2025) 
 
1 Yr
5 Yr
10 Yr
Government Money Market Portfolio
4.03%
3.03%
1.96%
For the seven-day period ended March 31, 2026, the Government Money Market Portfolio’s yield was  3.37%.
PORTFOLIO MANAGEMENT
Investment Adviser: Mason Street Advisors, LLC
Sub-Adviser: BlackRock Advisors, LLC
TAX INFORMATION
Shares of the Portfolio are offered only for funding variable annuity contracts and variable life insurance policies offered by The Northwestern Mutual Life Insurance Company through separate accounts. Insurance company separate accounts generally do not pay tax on dividends or capital gain distributions. Investors in variable annuity contracts and variable life insurance policies should refer to the prospectuses for the variable products for a discussion of the tax considerations that affect the insurance company and its separate accounts and the tax consequences to investors of owning such products.
COMPENSATION TO BROKER-DEALERS AND OTHER FINANCIAL INTERMEDIARIES
Neither the Portfolio nor any related companies pay compensation to broker-dealers or other financial intermediaries for the sale of Portfolio shares or related services. Investors in variable annuity contracts and variable life insurance policies should refer to the prospectuses for the variable products for important information about compensation paid to financial intermediaries for sales of variable annuity contracts and variable life insurance policies.
NMSF-SP3Northwestern Mutual Series Fund, Inc. Prospectus