James “Jimmy” Kent joins Downton in 1920 as footman alongside Sarah O'Brien's nephew Alfred Nugent. Ivy Stuart takes a fancy to Jimmy,and so does Thomas Barrow. Thomas at one point walks in on Jimmy (perhaps aroused) when he was shirtless, surprising him.
Jimmy is ambitious and in Carson's words, "sure of himself." O'Brien takes advantage of Jimmy's ambition after Thomas bullied her nephew. Whether she knows of Thomas' sexual orientation or simply suspects it, O'Brien urges Jimmy to stay close to Thomas due to his work experience and him being the lord's valet. Since Thomas is attracted to Jimmy, Thomas gladly takes him under his wing. Jimmy feels uncomfortable with Thomas' behaviour towards him but, initially, O'Brien dispels his concerns and encourages him to stay close to Thomas.
Jimmy's father died in the Great War, and his mother from Spanish flu. All he has left he tells Thomas are "cousins." He plays the piano, Anna remarking at one point it was nice to have another piano player downstairs, in reference to William Mason.
Jimmy previously worked as footman to the Dowager Lady Anstruther, and has a "natural air of confidence and grace" that Alfred does not have, and "takes the role of first footman, as a natural right, a bone of contention." Mr Carson insists he go by his proper name instead of his nickname upstairs. Jimmy is furious at that because he has never been called James in his life; even to Lady Anstruther he was called Jimmy. But Carson insists he is James now and will remain James as long as he at Downton. She wanted him to move with her to France, but he did not want to go, saying to Carson he did not think he would fancy the food. When he said to Carson that he knew how women can be, Carson said not as much as he thinks Jimmy did.
One night when Jimmy is asleep, Thomas sneaks in and kisses him thinking his feelings will be returned, but Jimmy is angry at Thomas for what he has done and Alfred catches him. Jimmy indicates he feels nothing for Thomas, leaving him devastated. After being encouraged to do so by O'Brien, Jimmy demands that Thomas be sacked and given no reference and threatens to inform the police of Thomas's actions if Mr Carson doesn't do so, fearing he will be suspected of being gay himself. His angry insistence on Thomas going alienated him from many other staff members, who cannot understand what is going on. Mrs. Hughes thinks Jimmy might have unintentionally led Thomas on, calling Jimmy "a vain and silly flirt" and a "young whipper snapper." He is later persuaded to let the matter drop, admitting that he personally never wanted to go as far as he did. In order to placate Jimmy and to get him to agree to work with Thomas in future, Lord Grantham informs Jimmy that he has been made first footman, much to the surprise of Mr Carson. Jimmy still is upset that Thomas is staying on.
In the 2012 Christmas Special Jimmy at first still appears uncomfortable around Thomas, not wanting to be seen to be alone with him or accept the gift of a drink when Thomas offers to buy everyone one. Later, whilst at the fair that most of the staff attend Jimmy wins some money betting on the Downton Abbey team in a tug of war match. At the last minute he asks Tufton to join them - a large man - and Downton wins and Jimmy wins his bet. He proceeds to get drunk and flash his money around and whilst he is walking alone two men attempt to rob him. Thomas appears and steps in to protect him and is beaten and robbed in his place after Jimmy runs away and leaves him. Jimmy fetches Dr. Richard Clarkson and some of the other staff for Thomas and stays silent whilst Thomas fails to say what really happened and so avoids telling everyone that Jimmy left him alone to face the two men and get beaten.
Jimmy later goes to see Thomas alone in his room and ask if he is alright. Jimmy says that Thomas was "brave" and that he feels bad for leaving him. Thomas reveals that he was following Jimmy that day as he had seen that Jimmy had had too much to drink. When Jimmy asks why he was doing this Thomas says that Jimmy "knows why", implying that he still has feelings for Jimmy. Jimmy says that he can never give Thomas what he wants. Thomas says that he understands and doesn't ask for it, but would like them to be friends. Jimmy says he can do that if it is only being friends and the scene ends on them chatting over a newspaper.
By 1922, Ivy it seems has captured Jimmy's attention. They dance, and later kiss when someone walks in on them in the downstairs boot room.