Originally from Sheffield, the Harrises moved to Weatherfield as part of the witness protection scheme in 2002, living under the name Nelson. After five months, their cover was blown and Tommy was shot in the arm while defending Katy from the Morgan brothers, gangsters who were after the family due to Angela helping to put their brother Tom behind bars for murder. After the showdown at No.6, the brothers were arrested and the Nelsons carried on living in Coronation Street, reverting to their true names.
In 2003, Katy got together with Martin Platt, a 35-year-old nurse. Decrying Martin as a pervert, Tommy refused to have anything more to do with Katy until they were no longer together. They caused a brief split from Angela, but they reconciled after Craig tampered with the brakes on Martin's car, nearly killing him and Katy. In 2005, when Tommy spread false rumours that Martin was having an affair with Sally Webster, Katy aborted her and Martin's child before learning the truth, causing Martin to finish with her. When Tommy gloated over what had happened, Katy became so enraged that she hit him over the head with a wrench, killing him instantly.
Tommy and his wife Angela, along with their children Katy and Craig moved to Weatherfield in November 2002, having rented 6 Coronation Street and using the surname "Nelson". They originally came from Sheffield where Angela worked in a pub. She witnessed a murder and gave evidence against the accused. The family of the accused took their revenge with threats and eventually tried to burn their house down. The Harrises were taken under the Witness Protection programme, given a new identity as the Nelson family and moved to Weatherfield.
Tommy was a trained mechanic (and Sheffield Wednesday F.C. supporter) and was soon hired by Kevin Webster at Coronation Street Garage, using references that the Witness Protection program supplied. Not long after, Kevin found a wallet containing a union card with the name "Tommy Harris" on it. Tommy took it when he found it lying where Kevin had left it but Kevin, when realising that Tommy had the wallet, accused him of stealing the wallet from a customer. Tommy couldn't explain and was sacked. Eventually however, Tommy took Kevin into his confidence and was re-hired.
In March 2003, Tommy was instrumental in helping fellow resident Martin Platt rescue his family when they end up being captured by notorious serial killer Richard Hillman, the former husband of Martin's ex-wife Gail who drove her along with the latter's son David, daughter Sarah, and granddaughter Bethany all in the canal. While Kevin was waiting to alert the authorities over the incident, Tommy helped Martin rescue his family from the surface before going back down to try and find Richard, only for his car to be empty, forcing Tommy to quickly return to the surface just as the emergency services arrived. Tommy was later commended for his heroic activities in saving Martin's family from Richard, who would be revealed to have drowned despite Tommy's earlier attempt to save him.
In April 2003, Katy slipped away to see her mates in Sheffield and was followed by the brothers of the man who was jailed on Angela's evidence. There was a showdown and Tommy was shot in the process, nearly losing his arm in subsequent surgery. The family stayed in Weatherfield even though their cover was blown and resumed using the name Harris.
Near the end of 2003, Tommy and Angela split up. Katy took up with Martin and though disapproving, Angela could not bear to be estranged from her daughter. Tommy was adamant that if Angela was going to keep in contact with Katy, he was not going to be a part of it. Angela left the house briefly but returned and insisted that Tommy left. Tommy began drinking and eventually Kevin had no choice but to let him go. Tommy lived in the flat over Street Cars, jobless for a while.
Shortly before Christmas 2003, Craig, upset that his family seemed torn apart because of Martin, rigged the brakes on Martin's car. He told his father what he'd done, but before it could be righted, they saw Katy drive off with Martin and they followed them. After Katy got out of the car, she saw her father following Martin and called him to warn him. She thought Tommy was going to kill Martin but Tommy was trying to get Martin's attention to make him pull over. The brakes failed before that could happen and Martin crashed the car. Tommy pulled him out before the car exploded but later took the blame for the rigged brakes so Craig wouldn't get into trouble. Craig couldn't handle the guilt and confessed to Martin who told the police he knew his brakes were bad and hadn't got them seen to. He made an uneasy peace with Tommy and Angela, but Tommy still didn't like Martin being with his daughter.
In 2005, Katy told Angela and Tommy that she was pregnant and they were not happy. In March, Tommy saw Martin and Sally Webster together and he thought they were having an affair. When Angela overheard something, she too believed it and they told Katy. Because her mother thought the affair was true too, Katy also believed it, left Martin and aborted their baby. Gail told Angela that Sally had an affair but it wasn't with Martin. Angela told Katy that Martin was not unfaithful which devastated Katy. Katy went back to Martin to tell him she was sorry but Martin dumped her. Katy then went to confront Tommy; he kept calling Martin names, so Katy got hold of a wrench, hit him over the head with it and killed him.
First and last lines
"Right, everybody out." (First line)
"Katy..." (Final line)