Born in Sydney, New South Wales, Brooks played his junior football for the Holy Cross Rhinos and Leichhardt Wanderers before being signed by the Wests Tigers. In 2012 he played for the Australian Schoolboys and also played in the Balmain Tigers' S. G. Ball Cup Grand Final win over the Canberra Raiders.
Having spent the pre-season training with the first-grade team, Brooks was receiving attention in the press, with Andrew Johns saying he was one of the best young talents he had seen in some time. Brooks played for the Tigers' NYC team in 2013. In April, Brooks played for the New South Wales U20s State of Origin team. On 29 July, Brooks re-signed with the Tigers on a 4-year contract.
In Round 24 of the 2013, Brooks made his NRL debut for the Wests Tigers against the St. George Illawarra Dragons. Although the Wests Tigers had exceeded their second tier salary cap, Brooks was given a special dispensation to play as neither team could make the semi-finals. Brooks scored a try and was awarded Man of the Match in the Tigers 34-16 victory, in what was described as, "a stunning NRL debut." The salary cap prevented Brooks from playing in any further games that year. At the end of the year, Brooks was named at halfback in the 2013 NYC Team of the Year.
Brooks became the Wests Tigers regular halfback for the 2014 season. Brooks finished off the Tigers year playing in 21 matches, scoring 6 tries and kicking 1 field goal. He was named 2014 Dally M Rookie of the Year.
In 2015, Brooks was selected on the interchange bench for the NRL All Stars team in the 2015 All Stars match, the youngest player to ever take part in the game. In the first half, he came on and played right centre. In the second half, he played five-eighth when Kieran Foran left the field injured. The Indigenous All Stars won 20-6.
Brooks finished the year with a personal best 10 tries from 23 appearances, the 5th highest amongst NRL halves. His 16 try assists were also the 5th most in the entire NRL for the year.