Sergeant Tom Hallett was part of Sergeant Lopé's security team aboard the colonization spacecraft USCSS Covenant. He was the husband of Sergeant Lopé. He was serving on the Covenant during its disastrous voyage to Origae-6, during which it suffered several catastrophes that resulted in the loss of most of the ship's crew and its hijacking by David.
Years prior to the voyage to Origae-6, Hallett had served under Sergeant Lopé on his security team. Despite their ranks, Hallett and Lopé fell in love and later became married. However, their love life never interfered with their professional life, as they knew they were security personnel before lovers. Hallett sometimes disagreed with what Lopé commanded of him, but he continued to follow orders. Weyland-Yutani later invited Lopé and Hallett's security team to secure and escort 2,000 colonists and crew members for a colonization mission to Origae-6 aboard the USCSS Covenant.
Before Hallett and the other crew members entered hypersleep, they partook in one last meal. Hallett spent the dinner by his husband's side. During the dinner, Covenant pilot Tennessee bet money on Hallett beating Lopé in an arm-wrestling competition, with Hallett losing to Lopé - and Lopé kissing him and telling Hallett he still loved him, which received glances from Oram and Karine. Tennessee made a comment on Hallett's sex life, which prompted Lopé to playfully invite Tennessee in a three-way, with Tennessee responding by claiming he would not only have sex with them but also ejaculate all over the table. Joking aside, the crew members enjoyed their last supper, listening to Daniels' speech about this mission. Hallett and Lopé were hand-in-hand at dinner - and with the rest of the crew, Hallett went into hypersleep.
Seven years before their arrival on Origae-6, a neutrino blast hit the Covenant while it was recharging via solar sails. The blast damaged the ship, killing dozens of colonists and forced the crew out of hypersleep. Hallett awoke, but Captain Branson was trapped within his sleep pod and was incinerated alive inside. Hallett, with Lopé, made security runs and held a brief funeral for the captain and all those who died. While repairing the ship, Tennessee found a recording of a woman singing - and it was traced to Planet-4, a nearby, hospitable, earth-like planet that would take several days rather than seven years to get to. Going on new captain Oram's orders, they reroute to Planet-4.
Hallett was part of the expedition that set down on Planet 4. On the way down via shuttle, Hallett has a panic attack while flying down, claiming he hates space. Lopé tries to comfort him and suggests that this anxiety was why he needed to do yoga. After landing down, Hallett followed Lopé's orders on securing the area and escorting the scientists to the signal. Lopé discovered wheat, and the life on the planet was found to be very similar to earth's, but no wildlife was present. The crew eventually traced the signal to a derelict spacecraft. Upon entering a corridor from below the ship, Hallett discovers a spore-like egg. Hoping to be known for a discovery, he probes the egg sack which release motes that invade his nose.
Moments later, after exploring the ship and exiting, Hallett falls sick from the motes in his body. As Lopé and the crew try to race him back to the med bay in the shuttle, the same situation is happening with Ledward, Karine, and Faris - as Ledward was infected and birthed a Neomorph which killed Karine. As the crew approached the shuttle, Hallett's condition worsened, and the shuttle exploded due to Faris' attempt at destroying the Neomorph. Moments later, Hallett started convulsing and screaming in agony, and seconds later a Bloodburster ripped its way through his throat and mouth, killing him.
Lopé mourned the loss of his husband, and Rosie comforted him. However, she told him there was nothing he could do for Hallett and that he was gone. After the battle with the Neomorphs, Lopé took Hallett's ring and went on with the mission.
It is likely that Hallett's body was later eaten by the surviving Neomorph.