He played GAA, soccer and rugby at De La Salle secondary school in Churchtown, but honed his rugby skills under Trinity College's director of rugby Tony Smeeth.
Adeolokun was also a very influential member of the Dublin University Sevens team that won back-to-back All Ireland Sevens Championships in 2011 and 2012.
Having recently completed his final exams at Trinity College, he will report to the Sportsground later this week for fitness testing with the rest of the Connacht squad.
Speaking from Galway, Connacht head coach Pat Lam said: "We're delighted to be able to give Niyi this opportunity. He was initially brought to our attention by Nigel Carolan last April when he started on the wing for the (Connacht) Eagles.
"He is clearly a brilliant broken-field runner with very good pace but we were also very impressed with what he offers in defence. With his raw talent and athleticism, we're looking forward to seeing how he performs in a professional set-up for the first time.
"When meeting with Niyi, I was struck by his maturity and also his unwavering determination to succeed after having overcome many challenges along the way. He is a good young man with excellent values and I know he will fit in very well to our team environment."
Tony Smeeth added: "I'm absolutely delighted for Niyi. He is a hard worker with a special talent and he deserves this opportunity.
"His rate of development was hugely impressive these past few years with Trinity but I know Connacht is the perfect place for him to step up that development even further. Training with professionals full-time and being around players like Mils Muliaina will be huge for him."
CONNACHT - 2014/15 SQUAD:
Hookers: Jason Harris-Wright, Dave Heffernan, Sean Henry, Tom McCartney.
Second Rows: Michael Kearney, Aly Muldowney, Michael Swift, Daniel Qualter, Quinn Roux.
Back Rowers: Andrew Browne, Mata Fifita, Jake Heenan, Willie Faloon, Eoin McKeon, John Muldoon, George Naoupu.
Scrum Halves: Kieran Marmion, Ian Porter, John Cooney.
Out-Halves: Miah Nikora, Craig Ronaldson, Jack Carty.
Centres: Robbie Henshaw, David McSharry, Conor Finn, Bundee Aki, Shane O'Leary.
Wingers: Fionn Carr, Matt Healy, Tiernan O'Halloran, Danie Poolman, Niyi Adeolokun.
Full-Backs: Mils Muliaina, Darragh Leader, Shane Layden.
- The Connacht Academy for 2014/15 will be confirmed in the coming weeks.