leighton was born in 1696, the fourth son and ninth child of sir edward leighton, 1st baronet, of wattlesborough in shropshire. he entered the army as a captain on 16 june 1716. in 1730 he transferred from major of barrell's regiment of foot to major of handasyd's regiment of foot, and on 6 july 1737 was promoted lieutenant-colonel of blakeney's regiment of foot. during the jacobite rising of 1745 leighton was sent with a considerable force from perth to hold the outpost of castle menzies. he was promoted colonel of the 32nd regiment of foot on 1 december 1747, major-general on 5 february 1757, lieutenant-general on 6 april 1759 and general on 25 may 1772.