The son of an Army lieutenant colonel, Richard Gregg followed his father’s footsteps and enjoyed a long career in the Army. After finishing his education at Trinity College, Dublin, and becoming a doctor, he was commissioned into the Royal Army Medical Corps (RAMC) as a lieutenant in 1907. He served with the British Expeditionary Force as a commanding officer at Field Ambulance units and saw service in India, Pakistan, Aden, France, Belgium, Shanghai, and Malta. Gregg retired in 1927 with the rank of lieutenant colonel (the same as his father). On retirement from the Army, he went to the Divinity School of Trinity College, and was ordained into Holy Orders on 1 July 1928. He took the curacy at Derryloran, County Tyrone and, after serving other parishes, was appointed Archdeacon of Elphin and Ardagh in 1940.
At Trinity College, Gregg captained the Dublin University Hockey Club. He made his Ireland début in 1907 and in 1908 helped his club side, Three Rock Rovers, beat North Down 6-0 to win the Irish Senior Cup. That same year Gregg played in both of Ireland’s matches at the London Olympics – the 3-1 win over Wales, when he scored one goal, and the 8-1 defeat by England in the final – and collected a silver medal. Gregg also played for and captained Leinster in inter-provincial matches. He later became an umpire.