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. Playing for the Tigers' NYC team, in April, he played for the New South Wales U20s State of Origin team. On 29 July, he re-signed with Wests 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 34-18 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.
2014
Brooks became the Wests Tigers regular halfback for the 2014 season. He played in 21 matches, scoring 6 tries and kicking 1 field goal. He was named 2014 Dally MRookie of the Year.
2015
In 2015, Brooks was selected on the interchange bench for the NRL All Stars 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.
2016
At the start of the season, Brooks had an option on his contract for 2017. Despite some offers from rival clubs and an attempt from the Wests Tigers to extend his contract, Brooks took up the option mid-season. He said, "My manager was in talks with a few clubs but it didn't come to anything and I was just happy to take an extension." With Wests Tigers struggling for wins mid-season, Brooks received some criticism from commentators such as Peter Sterling for his lack of involvement in games. Andrew Johns said, "He has to give his team more. He has got a lot of raps. There is talk he isn’t behind forwards going forward but he has to get his hands on the ball more … I don’t get it." Brooks' season was the hampered by a knee injury towards the end of the season, but the team recovered to be one win away from a semi-final berth. He later admitted, "I wasn’t playing my best footy." Brooks scored 5 tries from his 21 games for the year.
2017
In March and April, Brooks, alongside Tigers captain Aaron Woods, halves partner Mitchell Moses and superstar fullback James Tedesco, attracted media speculation about where the players, dubbed the "Big Four" would play after all of their contracts with the Tigers were set to expire at season's end. On 18 April, Brooks extended his stay at the club to the end of the 2019 season, the only player of the group to re-sign. At the time, Brooks was sidelined from the game for 4 weeks due a hamstring injury. He made his return in Round 8, having a great match, leading the team and setting up the winning try for Kevin Naiqama in the Tigers 18-12 thrilling win.
2018
With Wests Tigers winning 5 of their first 6 games, Brooks was described as the most improved player at the club. "The 23-year-old looks a completely different player this year – stronger, faster and fitter, exploding with confidence, running the ball more than ever before. His average run metres have shot from 75 to 106 so far and his eight drop outs forced in six games has already equalled his entire 2017 tally of eight in 17 games. His 20 tackle busts is just two short of his 22 busts in 2017 as well." Elsewhere it was said he, "looks more confident and assured, is defending better, making better decisions and running the ball more." Brooks was one of two players who appeared in all 24 games for the Tigers, scoring 5 tries an kicking 2 field goals. At the Dally M Awards, Brooks placed third overall, and was named the competition's Halfback of the Year. On December 3, Brooks re-signed with the Wests Tigers for 5 years. Keeping him at the club till the end of the 2023 season.
2019
By round 24, Brooks held the statistic of the current player with the most NRL caps to not have played finals football, a record that would continue with Wests Tigers finishing ninth. Brooks finished the season making 24 appearances and scored 4 tries.
