The Suns have signed the 185cm midfielder/forward to a three-year contract rather than the standard two-year deal offered to most draftees.
Sexton is a member of the AFL/AIS Academy and has been a supplementary list player at AFLQ club Redland and a Suns reserves top-up player this season.
He toured Europe with the Academy squad earlier this year, won the Alan McLean Medal as the division two best and fairest and the Queensland MVP at last year's under-16 national championships, and was a Queensland under-18 representative this year.
Gold Coast list manager Scott Clayton said Sexton had been on the club's radar since his standout performance at the 2010 under-16 national carnival.
"Alex looks a real player, we have been thrilled with the way he has developed, and his football has continued to impress us," Clayton said.
"Being eligible to be selected as a Queensland zone selection, we have been fortunate enough to have spent a lot of time with Alex, he knows our program, players and coaches.
"From a football perspective he has real composure, an attack on the footy, and his speed and kicking under pressure is great.
"At 185cm, Alex is a great size, and he has all the attributes, we believe he will develop into a perfect midfielder for us."
Sexton, who is studying Year 12, said he was rapt to be joining the team he trained with over the pre-season.
"Gold Coast is one of the most exciting teams in the competition, and having had the chance to train and play with the reserves I just can't wait to get down there," Sexton said.
