McNamara's first win as an apprentice jockey came in 2007 when riding Prince Livius at Tipperary for trainer Tom Hogan. The following year he was champion Irish apprentice jockey.[3]
In 2014 he started working for trainer Aidan O'Brien at Ballydoyle, where he was a work rider as well as riding in races. In 2015 he won the Group 2 Beresford Stakes at the Curragh Racecourse on Port Douglas and in 2017 he won the Group 3 Derrinstown Stud Derby Trial on Douglas Macarthur.[3] McNamara combined his riding with studying at Griffith College Dublin, graduating with a first-class honours degree in accounting and finance in 2018.[4]
On 27 June 2020 McNamara rode Tiger Moth for O'Brien in the Irish Derby and was beaten by a head by stablemate and favourite Santiago. A few days later he was offered a ride in the Epsom Derby on Serpentine, one of O'Brien's six runners in the race. It was his first ride in the Derby, which was held on 4 July, having been postponed due to the COVID-19 pandemic. For the same reason it was being held without spectators (behind closed doors). Serpentine, who went off at odds of 25/1, soon established an unassailable lead and stayed on to win by five-and-a-half lengths. It was McNamara's first win since the previous October, and provided O'Brien with a record eighth Derby win. After the race McNamara said: "All I heard was the horse breathing. I got a little bit of a freebie. Aidan said go your own tempo give him a breather and then keep going. He was right."[2]
