Rex began his career in the youth ranks of Bath City before moving on to the Academy at Bristol City. He then moved on to Oxford United at the age of 16, where he signed a scholarship and progressed into their under-18s.
After leaving Oxford in 2018, he joined Southern League Division One South side Bristol Manor Farm in March 2018, where he made 10 appearances and was an unused substitute 14 times, assisting one goal.
In October 2018, Southern League Premier Division South side Frome Town came calling. Rex went on to become a vital component of Frome’s side over the next three-and-a-half years, scoring 31 goals and assisting 15 from wide areas in 124 games while being an unused substitute three times. While at Frome, he helped them reach the Southern League Division One South Playoffs in 2022 before a semi-final defeat to former side Bristol Manor Farm.
His form for Frome saw him handed a chance with National League South club Bath City in June 2022. During the first half of the season, Rex scored three goals and assisted five for the Romans in 16 games while being an unused substitute 14 times.
In February 2023, he was loaned out to Southern League Premier South side Yate Town for an initial month before the loan was extended for an additional month, where he scored one goal in nine appearances.
During the middle of April 2023, Rex returned to parent club Bath City where he made a further two appearances and was an unused substitute once, featuring as a 52nd minute substitute in the triumphant Somerset Premier Cup final win over Paulton Rovers at The Optima Stadium.
He departed Bath in May 2023.
In July 2023, Rex signed for the Seagulls after featuring on trial for the club during pre-season.