The 30-year-old came through the ranks at Arsenal where he enjoyed loan spells at Millwall, West Bromwich Albion and Queens Park Rangers before he left the Emirates in 2010 to sign for Hull City.
Simpson spent three years with the Tigers, and made 86 appearances in Humberside before he made the move to Thai side Buriram United where he spent a year.
Upon his return to the UK in 2014, he signed for Orient and in his second season became just the 11th forward in the Club’s history to reach 20 league goals in a season.
Simpson went on to score a further five League Two in that 2015/16 season and was rightfully named in the PFA Team of The Year.
He departed E10 in 2017 after three years, 99 appearances and 36 goals to play in the MLS for Philadelphia Union.
Simpson made 34 appearances in his two years in America but returned to the UK following the end of his contract and began training with the O’s to keep fitness.
He impressed while at the Club and agreed a deal to keep him at The Breyer Group Stadium until the end of the season.
Jay told leytonorient.com: “I’ve been training here for a while, I’m looking forward to getting started and looking forward to the challenge and the final push to try and get us over the line”.
The forward added: “I like the group of boys and I really like Justin [Edinburgh]. I have a lot of respect for him also I know the Club and the people at the club, which is part of the reason why I was looking forward to coming back.”
The deal is subject to international clearance as Simpson last played competitive football for Philadelphia Union in the MLS.