Mullagh learned cricket on the Edgars' Pine Hills agricultural property at Harrow in Victoria's Western District, where Aboriginal stockmen of the Jardwadjali and surrounding nations had been playing against settlers for at least a decade by the mid-1860s. Coached first by Tom Wills at Edenhope in 1866-67 and then by Charles Lawrence, Mullagh emerged from the Boxing Day match at the MCG in December 1866 as the team's leading batsman and most accurate bowler. On the 1868 English tour he played in every one of the 47 fixtures and was almost the entire side single-handedly. His 1,698 runs across the summer included one century and seven fifties; his 245 wickets, taken at an average of 10, were almost twice the haul of any other Aboriginal bowler. He bowled long spells of round-arm — his 1877 figures recorded 831 maidens in a season — and had the wristy free action that contemporaries said reminded them of the best English professionals. Tarrant, the fearsome Cambridgeshire fast bowler, paid him the most-quoted compliment of the tour. After Tarrant bowled to Mullagh during a lunch interval at one of the matches, he is reported to have said: 'I have never bowled to a better batsman.' Mullagh continued to play for Victorian sides into the 1870s, including a one-off appearance for Victoria against Lord Harris's English touring team in 1879, and went on representing district sides almost to the end of his life. He died at Pine Hills station the day after his 50th birthday in August 1891 and was buried in the Harrow cemetery.