O'Nien has signed on a two year deal for a fee rumoured to be around £380k, which, if true, is looking to be an absolute bargain.
The 23-year-old played a vital part of the Chairboys' promotion to League One last season, bagging eight goals and four assists. A very successful campaign for the young midfielder saw a host of clubs keen on snapping him up, but O'Nien was quick to decide on Sunderland as his next adventure.
Speaking to the club following his arrival on Wearside, O'Nien said:
"It's a huge honour because it's such a big club.
The last few days have been pretty manic for me and it's all happened so fast, but I'm delighted to be here, and I can't thank the club enough for giving me the opportunity."
O'Nien is likely to provide us with an exciting partnership in midfield with fellow new boy Dylan McGeough, and it looks like Lee Cattermole is going to struggle to get a look in if he opts to stay with the Black Cats.
The midfielder signed for Wycombe in 2015 following his release from Premier League side Watford and went on to make 119 appearances for Gareth Ainsworth's side. Despite being only 23 years old O'Nien clearly has his head screwed on and has the motivation and determination that we need from our players, stating in an interview on www.tremr.com that:
"To be a footballer you have to train to be like Ferrari. You have got to put your body into the best possible condition to perform. You can't use the wrong fuel in a Ferrari otherwise it wont go. The same goes to me. I must fuel my body properly."
Wise words, Luke. If you say you aren't excited about this lad's arrival then I don't believe you.