He was born in 1588 the son of Andrew Knox, Bishop of the Isles, and Elizabeth ("Bessie") Knox, his cousin. He was educated at Glasgow University graduating MA in 1608.[1]
He received crown provision to the Deanery of the Isles on 4 August 1617[2] and started serving as a minister on Tiree in 1618. He is the first Dean of the Isles to be known by name (apart from the famous Dean Monro, a century earlier), though an unnamed cathedral dean was recorded in 1572, and the "dean and chapter of Iona" are attested again on 5 June 1576.[2]
On 24 February 1619 he was granted crown provision to succeed his father as Bishop of the Isles, his father later becoming Bishop of Raphoe in Ireland.[3] Thomas Knox's last historical appearance dates to 1 November 1627, a year later than the date given by Robert Keith.[4] He had died by 3 April 1628, meaning he almost certainly died earlier in that year or at most in 1627.[5]