Sir Thomas was second son to Sir Ralf Lovell of Barton Bendish, Norfolk, and had joined Henry Tudor as an esquire during his exile in France. He fought at Bosworth (1485), when Henry landed on the south coast with a couple of thousand French mercenaries and a few Lancastrian knights, gathering more support on their way north. Richard III was slain, and the battle was ended amidst Yorkist treachery and desertion. Lovell also fought at the battle of Stoke in 1487, when the pretender Lambert Simnel, already crowned King of England in Dublin by his supporters, was finally routed, and the Tudor dynasty was safely assured. Lambert Simnel is said to have attended Sir Thomas's funeral in 1525, as he was the last survivor of Stoke, although they fought on opposite sides. Lovell was knighted by Henry VII for his prowess. His elder brother Sir Gregory was made banneret at Stoke as well.

He entered Parliament as M.P.. for Northamptonshire in 1485, presumably with a great reputation already, for he became Speaker of the House of Commons from 1485-88. He was still a plain esquire, not being knighted until 1487. In 1485 he was also appointed Chancellor of the Exchequer for life, with an annuity .

Later he had many court appointments - among them as President of the Council in 1502, and Constable of the Tower in 1509. During his lifetime he was one of the most powerful men in the country, a confidant of and advisor to the king.

Sir Thomas was made K.G. in 1498, (his stall plate is on the north side, Stall No. 13); Henry preferred to use the Garter to reward his closest associates and advisors, creating 37 new Garter Knights. In comparison, only Bray became a baron by charter. (Chrimes, ibid).

He built the gatehouse at Lincoln's Inn, placing his own and Henry VIII's arms on it; and also built East Harling manor, with his arms on that. He endowed a nunnery at Halliwell, near Enfield, and he was buried there in 1524 with his wife, Isabel, daughter and co-heiress of Lord Roos of Hamlake.