the lower decks

The series is set in 2380, one year after the film Star Trek: Nemesis (2002), and, unlike typical Star Trek series, focuses on the support crew of a starship rather than the main bridge crew.[15] McMahan set the series shortly after Nemesis, the last Star Trek film in the Next Generation era, due to his love of The Next Generation.[5] The series is named after the Next Generation episode "Lower Decks", which also focuses on the lives of lower-ranking starship personnel and which McMahan said was his favorite episode of any Star Trek series; the episode was the first thing McMahan showed the Lower Decks writers room when they started work on the series.McMahan was inspired by the social side-stories in episodes of The Next Generation, with Kurtzman explaining that the "A story" of a typical Star Trek episode would be taking place in the background of each Lower Decks episode, so "huge, crazy, crazy shit is going on in the background and that's super peripheral to the story that you're actually focusing on". Kurtzman felt this made the series a unique addition to the franchise Starting in late 2019, astrophysicist Erin Macdonald joined the Star Trek franchise as a science advisor. Macdonald said each series was on a "spectrum of science to fiction" and the Lower Decks writers approached science from the perspective of "we can get away with a lot more" than the live-action series, so her role was mostly to fix small dialogue mistakes to ensure the correct terms were being used

The main setting of the series is the starship USS Cerritos, a "California-class" ship. This ship class, created for Lower Decks, is a class of support starships that work with larger starships like those seen previously in the franchise, but are not "important enough" to have appeared on screen before. McMahan described the mission of the Cerritos as "Second Contact": after Starfleet has made first contact with a new alien civilization and invited it to join the Federation, the crew of support ships like the Cerritos arrive to find "all the good places to eat [and set up] the communications stuff" McMahan wanted California-class ships to be named after Californian cities, and chose the city of Cerritos because he otherwise only knew it for local Cerritos Auto Square car dealership advertisements. He wanted to give the city "one more thing other than just being the home of the Auto Square".

McMahan did not want the humor to be "punching down on Trek" and focused on telling Star Trek stories where the characters happen to be funnyWriters from different comedic backgrounds and with different levels of Star Trek interest were hired.Kurtzman described Lower Decks as a love letter to Star Trek and it is filled with many references to other Star Trek series. McMahan said these were there to "create a rich, vibrant, fun expression of the world of Star Trek in that era" rather than just be Easter eggs for fans to pick through. It was important to the team that these not distract from the emotional storytelling and also fit within established canon, with Star Trek author David Mack consulting on the series to ensure that it fit into the franchise. McMahan hoped that references to The Animated Series specifically would honor it as the franchise's first animated series. The characters often use the real-world titles of past Star Trek episodes when referencing those events, with McMahan explaining that the personal logs of famous characters are given similar in-universe titles to the episodes they are from. The franchise established that "Star Trek characters watch Star Trek" in the series finale of Star Trek: Enterprise, where the events of an earlier mission are recreated with a hologram, and McMahan felt many events from past series would be common knowledge within Starfleet. Acknowledging this allowed the main characters to be "geeks for Star Trek", which let Lower Decks be a "Rosetta Stone" connecting all previous Star Trek projects.

Beckett Mariner: A human ensign aboard the USS Cerritos and the daughter of Captain Freeman.Newsome described Mariner as an irreverent rule-breaker who has been demoted several times, though she is actually "very good at all things Starfleet"The character is named after showrunner Mike McMahan's sister, Beckett Mariner McMahan.

Brad Boimler: A human ensign aboard the Cerritos, Boimler is a stickler for the rules and will need to learn how to improvise if he is to become a captain one day. He is later promoted to Lieutenant Jr. Grade in Season 4. Quaid said the character would "nail the written portion of the driving test with flying colors but once it actually got to him being in the car, it would be a complete and total disaster."

D'Vana Tendi: An Orion ensign in the medical bay aboard the Cerritos,Tendi is a big fan of Starfleet, and is thrilled to be on a starship. She is new to the Cerritos at the start of the series, and helps introduce the audience to the setting and characters. McMahan said he would act like Tendi if he ever got to work on a starship.

Sam Rutherford: A human ensign aboard the Cerritos, Rutherford is adjusting to a new cyborg implant McMahan compared Rutherford to the Star Trek: The Next Generation character Geordi La Forge, saying they are both "amazing at engineering stuff" but Rutherford does not always solve the problem like Geordi because he is still learning.

Carol Freeman: The human captain of the Cerritos and Mariner's mother. McMahan described her as a capable Starfleet captain whose starship is not very important. Freeman does not want Mariner to be on the Cerritos and is looking for a reason to have her transferred to another ship.

Jack Ransom: The human first officer of the Cerritos whom McMahan compared to Next Generation's William Riker, if he was on speed and had less shame

Shaxs: A Bajoran tactical officer aboard the Cerritos. At the end of the first season, Shaxs dies sacrificing himself for Rutherford but returns in the second season in a storyline that plays on the numerous times and ways that characters have been resurrected in previous Star Trek series.

T'Ana: A Caitian doctor and head of medical aboard the Cerritos.McMahan described her as a "good doctor, but she's an unpleasant cat". Including a Caitian in the series is a reference to Star Trek: The Animated Series which also features a member of that species, M'Ress.