[3] Brooksby enrolled at Baylor University to play college tennis, but turned pro after he redshirted his freshman season due to injury.

[4] On August 12, 2018, Brooksby defeated Brandon Nakashima to win the USTA Boys' under-18 national championship.

[7] On August 23, 2019, Brooksby qualified for the main draw of the US Open, where he defeated Tomáš Berdych in four sets in the first round.

He also reached his first ATP tour final at the 2021 Hall of Fame Open in Newport, defeating Evgeny Donskoy,[11] Denis Kudla,[12] Peter Gojowczyk,[13] and 7th seed Jordan Thompson.

[17] He beat John Millman[18] to advance to his first ATP 500 semifinal, where he lost to 5th seed (and eventual champion) Jannik Sinner.

[20] The following week at the 2021 National Bank Open, Brooksby made his debut at ATP 1000 level but lost in the first round to Nikoloz Basilashvili.

He reached the fourth round of a Major for the first time, defeating Mikael Ymer,[22] compatriot Taylor Fritz,[23] and 21st seed Aslan Karatsev.

[24] Brooksby, aged 20, became the youngest American to reach the US Open fourth round since a then 20-year-old Andy Roddick did so in 2002.

Brooksby defeated Karatsev in the 31st five-setter of the tournament – tied with 2015 Wimbledon for most at a Grand Slam event, since 34 at the 2004 US Open.

At the 2022 BNP Paribas Open, Brooksby reached the fourth round of a Masters 1000 for the first time in his career, defeating World No.

[29] He repeated the feat at the 2022 Miami Open reaching the fourth round in his consecutive Masters 1000 where he lost to the top seed and World No.

[38] In July, it was announced Brooksby would receive a provisional suspension from the International Tennis Integrity Agency after he was alleged to have missed three doping tests.

[41][42] In February 2024, the International Tennis Integrity Agency announced an agreement with Brooksby that reduced his suspension to 13 months, making him eligible to return to competition on March 3, 2024.