Thomas Wellington is the father of Trish and Shea. He is a real-estate mogul with money to burn. He doesn't believe Henry Dunn fits into their family and wishes to stop the wedding at all costs. Thomas is impaled by a head spade in "Thwack".
Thomas is paying Hunter Jennings, Trish's old boyfriend, to break up Trish and Henry Dunn. Uncle Marty overhears a discussion between the two and confronts Thomas about it.
In Episode 3, Thomas' plan to break up the wedding unravels when Henry finds out about it and Hunter gives up. He forces Mr. Wellington to pay him, or else he'll tell Trish the truth. Thomas finally gives in and meets Hunter on the docks, giving him the required some of money in exchange for Hunter never speaking to Trish again.
In Episode 5, Thomas is going on a bike ride with Trish when the two of them are suddenly hit by a rigged log trap set up by Cole Harkin. While they are patching up, Trish finally confronts her dad over his mistrust of Henry. Thomas responds that he "doesn't trust the boy" based on instinct. He then says that his instincts have gotten him where he is today, but Trish snaps and tells him that his instincts suck. The injured pair notice Cole and try to get his attention, but he instead sets his attack dogs on them. Thomas defends his daughter and manages to kill one of the dogs.
In "Thwack," Thomas comes to the altar to mimic lighting the unity candle during the wedding rehearsal. Abby Mills is sent to turn off the lights, which releases a head spade from the chandelier above the altar, splitting Thomas' head open down to the neck in front of the wedding party.
- Mr. Wellington's death is a crucial turning point in the plot, as it is the moment where the rest of the characters finally discover that a killer is loose on the island.
- Richard Burgi, the actor who played Thomas, was the only cast member in the series to be told by the writers of his death before that day's script had been handed out, due to the fact that his demise is crucial to the story.
- Mr. Wellington was the only character to ever piece together that something was wrong with Henry.
- Mr. Wellington is the last member of the wedding party to die who didn't realize that a killer was on the loose (his death is actually what lets the other characters know of this).