The 24-year-old, who has played 45 times for Ulster since making his debut in December 2011, will join the Scottish club on a two-year deal through to May 2017 after being linked with a move to Scotland last week.
Edinburgh have played some brilliant rugby this year and shown the potential of being a very, very good side.
Comfortable at centre and on the wing, Allen has found his chances at Ulster become increasingly frustrated by several internationals, including Tommy Bowe, Andrew Trimble and Darren Cave, ahead of him in both areas of the field.
Limited to just eight appearances for the Irish province so far this season and with Charles Piutau set to arrive at the club in 2016 from New Zealand, the former underage and Emerging Ireland prospect has decided to seek a new challenge elsewhere.
Edinburgh have spent most of the current season limited to just four front-line centres and with Scotland international wing Tim Visser leaving the Scottish capital to join Harlequins this summer, there is also potential vacancy on the left wing.
“Edinburgh have played some brilliant rugby this year and shown the potential of being a very, very good side,” Allen said.
“I think the ethos, the fitness, the physicality, everything – from what I can see the team pride themselves on being the best defensively, the fittest and the most disciplined, and I’m just looking forward to getting stuck in and trying to spring anything I can.”
A former pupil of Methodist College Belfast along with team-mates , Allen was man of the match as he helped his side win the Ulster Schools Cup in 2008 and 2009.
Citing Jonah Lomu, Jonny Wilkinson and Matt Giteau as three of his rugby heroes, Allen admits that he is happy to play at centre or wing as required, and he is looking forward to the new challenge that awaits him despite his love for his hometown.
“I’ve never lived anywhere else, always been in Belfast, and I’m probably a bit of a homebird,” he added.
“I do love the city and everything that comes with it, but I’m looking forward to making a change, starting afresh.
“Apart from playing Edinburgh at BT Murrayfield over the last few years, I’ve only ever to been to the city twice to visit, both times with rugby school tours when we played Merchiston Castle School.
“I’m really looking forward to moving to the city, I’m really excited. It looks like an incredible place to live.”
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