A senior officer denotes a member of the senior staff of a starship or starbase involved in the top level, command decisions of the day-to-day operations of their post.

In the Earth Starfleet, where there were limited personnel choices with special talents, junior officers by rank were sometimes senior officers by practicality. Some such personnel included:

• Ensign Travis Mayweather, pilot of the Enterprise NX-01, experience with other worlds, as part of the Earth Cargo Service
• Ensign Hoshi Sato, communications officer of Enterprise, exceptional linguistic abilities
• Lieutenant Malcolm Reed, armory officer on Enterprise', chief of security

In the Federation Starfleet, senior officers usually included officers with the rank lieutenant commander or above and could include, but was not limited to (regardless of rank):

• Commanding officer
• Executive officer
• Operations manager
• Chief engineer
• Chief of security
• Chief medical officer
• Science officer

The commanding officer could also add certain officers at his or her discretion. These officers had the privilege of sitting in with the senior staff during briefings, or at times had the ear of the commanding officer.

Some of the more permanent additions have included:

• Commander Deanna Troi, ship's counselor, USS Enterprise-D / USS Enterprise-E
• Lieutenant Tom Paris, flight controller, USS Voyager
• Seven of Nine, astrometrics laboratory supervisor, USS Voyager
• Ensign Harry Kim, operations officer, USS Voyager

Occasionally, one is referred to as a senior officer in a manner that is equivalent to a ranking officer. Both B'Elanna Torres and Tuvok tried to take responsibility as the senior officer in the installation of a spatial trajector without Captain Kathryn Janeway's consent. (VOY: "Prime Factors")