On stage Ajala has performed in Nation, A Midsummer Night's Dream with the Royal Shakespeare Company, Hamlet, and as Jim Brown in the European premiere of Kemp Powers' One Night in Miami.
In film, his first part was in Kidulthood, and he also appears in the sequels, Adulthood and Brotherhood; he has also appeared in The Dark Knight and in major roles in Starred Up and the 2016 Seekers. On TV he has appeared in many series including Doctor Who and in major roles in Black Box, Beowulf: Return to the Shieldlands, Nightflyers, and Falling Water.
Sean 'Mac' McAlister, a character from 2017 video game Need for Speed Payback, is voiced by him.
Ajala has appeared as Keith in the BBC Radio 4 dramas Burned To Nothing (2011) and Felix in The Price of Oil: Someone's Making A Killing In Nigeria both by Rex Obano.
In 2018 Ajala was cast in season 4 of Supergirl, portraying Manchester Black.