Born in Derry on 5 October 1881, Tegart was the son of a Church of Ireland clergyman, Rev. Joseph Poulter Tegart of Dunboyne, County Meath, and his wife Georgina Johnston. He was educated at Portora Royal School, Enniskillen and briefly at Trinity College, Dublin. He retained contacts there and was awarded an honorary doctorate in 1933. Prior to his roles in India, he served as chief assistant to Ormonde Winter, the head of British Intelligence operations in Ireland during the Irish War of Independence.
