The Federation Merchant Service, colloquially known as the Merchant Marine (a term dating back to pre-space Earth's ocean-going merchant fleets), consists of commercial vessels of Federation registry. Vessels of planetary registry are not part of the Federation Merchant Service, but may be part of the planet of origin's merchant fleet. Planets which maintain a merchant service are Earth, Vulcan, Andor, Alpha Centauri and Betazed, among others. Of the Federation's founding planets, only Tellar does not maintain an official merchant service.

The Romulan Star Empire maintains a tightly controlled merchant service, while in the Klingon Empire, merchant fleets are maintained by individual Houses. The Ferengi also maintain a merchant service consisting of all Ferengi commercial vessels, centrally controlled by the FCA. Other stellar nations have varying types of merchant fleet organisations.

Federation Merchant Service uniforms are similar to those of Starfleet in cut and quality, but the colours are distinctive to the Service. As with Starfleet, the three divisions of the Merchant Service wear separate colours: red for Deck Division (equivalent to Starfleet's Command Branch), yellow-gold for Operations Division, and blue for the Purser's Division.

Passenger ships have a variety of uniforms for stewards and other members of the Purser's Division, specific to both the theme of the ship's decor and to the duties of the individual. A ship with a tropical theme may have the bartenders wearing Earth Hawaiian shirts, swimming instructors wear swimsuits, and so on...

The Merchant Service insignia is incorporated into the combadge and is worn on the left breast. It consists of a golden disc with a silver arrowhead in the centre, similar to the Starfleet insignia. The combadge does not have many of the more specialised functions of the Starfleet version, but does include communications, transporter locator and security access features.

Rank insignia is worn on the right collar of the pullover. Officers wear a series of gold and gold-rimmed black pips, while ratings wear an embroidered patch with a series of diagonal stripes and Bosun's Mates wear an embroidered patch with a series of chevrons. Bosuns wear a single gold-rimmed black pip.

Cadets at the Merchant Academy wear a series of vertical silver bars denoting their academic year. Fourth year cadets serving on their cadet cruise are addressed as midshipmen.