Company: MRCY
Filing Date: 2025-11-05
Form Type: S-8
Source: 0001049521-25-000070
Chunk: 0

Company: MERCURY SYSTEMS INC
Filing Date: 2025-11-05
Form: S-8
Chunk 0
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<div align='center'>As filed with the Securities and Exchange Commission on November 5, 2025</div>

#### Registration No. 333-

### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, D.C. 20549

#### FORM S-8

### REGISTRATION STATEMENT

#### UNDER

#### THE SECURITIES ACT OF 1933

#### MERCURY SYSTEMS, INC.
<div align='center'>(Exact Name of Registrant as Specified in its Charter)</div>

| Massachusetts                                                  |     |                             04-2741391 |
| (State or other jurisdiction of incorporation or organization) |     | -I.R.S. Employer Identification Number |
| 50 Minuteman Road                                              |     |                                        |
| Andover, Massachusetts                                         |     |                                  01810 |
| (Address of Principal Executive Offices)                       |     |                              -Zip Code |

#### MERCURY SYSTEMS, INC.

#### 2025 Long Term Incentive Plan
<div align='center'>(Full title of the plan)</div>

#### Stuart H. Kupinsky
<div align='center'>Executive Vice President, Chief Legal Officer, and Corporate Secretary</div>

#### Mercury Systems, Inc.

#### 50 Minuteman Road

#### Andover, Massachusetts 01810
<div align='center'>(Name and address of agent for service)

(978) 256-1300

(Telephone number, including area code, of agent for service)</div>

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

| Large accelerated filer [X] |     | Accelerated filer []         |
| Non-accelerated filer []    |     | Smaller reporting company [] |
|                             |     | Emerging growth company []   |

| If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.  [] |

### EXPLANATORY NOTE
This Registration Statement is being filed solely