 He succeeded to the Scottish peerage title as 3rd Lord Bruce of Kinloss in August 1613, aged 13, on the death of his elder brother, Edward Bruce, 2nd Lord Kinloss, killed in a duel with Edward Sackville, 4th Earl of Dorset.The family estates included Whorlton Castle and manor given to his father by King James I of England in 1603.The King granted the wardship of Thomas and the estates to his mother Magdalene, until he came of age at 21.