The 19-year-old joined the club on loan from Premier League new boys Huddersfield Town late last season, and now makes the switch permanent after a successful trial spell.
A combative central midfielder who is equally comfortable in defence joined Mark Bower’s Avenue in March, featuring in the final two matches of the season.
Prior to his move to the Horsfall Stadium, Spencer lined up for Huddersfield’s under-23 side, having captained their under-18s and duly earning his first professional contract.
He has featured heavily as a trialist throughout the summer, and Bower was keen to tie him down to the club for the coming season.
“Jamie came in at the back end of last season and did well for us,” the Avenue manager told the club`s official website. “He played the last two games and impressed us with his performances.
“We knew he was going to be available in the summer having been released by Huddersfield, so we wanted to get him in and give him a chance.
“Obviously all the fans have seen that he’s been here on trial throughout the summer, but he was always one we wanted bring in for the start of the season.
“Jamie is keen to do well and keen to learn, we have a lot of experience in the team so he is one that can learn from them.
“And I see no reason why, once he gets in the team and puts a run of appearances together, he can’t attract attention from higher up the ladder.
“The challenge is there for him to get back into the Football League, hopefully we can be the platform for him to showcase his talents.
“But it is now down to him to play well, and all young players have ambitions of playing in the League, and hopefully he can help us along the way.
“I think with the qualities he’s got, he has the potential to get himself back up there, playing football at a much higher level”.