The 23-year-old started his career at Stoke City, where he enjoyed loan spells at Scunthorpe United, Mansfield Town, Forest Green Rovers and Accrington Stanley before making the move to Ipswich Town in 2015.
The Southwark-born striker scored on his debut in the League Cup win over Doncaster Rovers, but made no other appearances before joining Chester FC.
It was at the Blues where Alabi had his best career spell to date, scoring 18 goals in 46 games in the 2016-17 season as he helped keep the Cheshire side in the National League before completing a move to Tranmere Rovers for an undisclosed fee.
Alabi told leytonorient.com, “I’m buzzing to get it over the line. It was an easy decision for me and I can’t wait to get going… My ambition is to get as many goals as I can, and the biggest ambition for me is to get this Club promoted back to the Football League.”
Head Coach Justin Edinburgh said, “He’s got a lot of attributes that you look for in a new signing. First and foremost, his work ethic is excellent, while physical attributes are a big positive. He’s got pace and power and is a good finisher.
“The Club were interested in signing him last season but I believe the fee got in the way so when we were made aware of his availability, we jumped at the chance. We saw off a lot of competition to sign him and once I had met with him face-to-face, I had no hesitations”
Alabi will be wearing the 27 shirt next season.