Fletcher attended Starfleet Academy where he became friends with Brad Boimler. According to Boimler, "Fletcher's like a natural peace negotiator. He was always getting us out of trouble back in the Academy."
One week after the Temporal Edict was implemented, he frantically attempted to repair an access panel in one of the ship's corridors while he carried a PADD and an armload of ship parts. When his time ran out, he threw all the parts into the panel and ran off to his next assignment. (LD: "Temporal Edict")
After the Cerritos was exposed to an ancient generation ship's terraforming emulsion, he was in one of the ship's corridors, being assisted with walking by a sciences ensign, when Ensign Beckett Mariner released parizene gas, and neutralized the terraformation. (LD: "Moist Vessel")
Later that year, he was working with Mariner and Boimler reprogram the ship's isolinear cores. He later imprinted his brain patterns onto one of the core, essentially giving it life. During this time the Cerritos was involved in an encounter with a Drookmani ship, which was later infiltrated by the core after it was jettisoned from the Cerritos' airlock.
As explained by Mariner to Commander Ransom, and later passed along to the rest of the crew, "Ensign Fletcher's brilliant improvisation, updating the isolinear core to weaponize it against the Drookmani saved the Cerritos. Fletcher demonstrated the sort of selfless heroism that Starfleet's all about. It's that heroism that earned him a promotion and a transfer to the Titan!" (LD: "Terminal Provocations")
Fletcher's stint as a lieutenant aboard the Titan lasted a mere six days, and after he was caught throwing garbage into the ship's warp core he was demoted back to ensign, fired, and sent back to Earth.
In "Terminal Provocations", Fletcher was voiced by Tim Robinson. Fletcher has no lines in the other episodes in which he appears.
Lower Decks executive producer Mike McMahan said, "We have this character Fletcher where he's kind of like our dark version of Barclay. Barclay was not a great officer, but then when everybody came together and believed in him, supported him instead of being frustrated by him, he was able to find his path. Fletcher is the opposite, not able to do that with the people supporting him and try to work with them, which is why he ends up not in Starfleet at the end of the day."