O’Kane, who was in the final 18 months of his previous deal, has committed his future to the Cherries until the summer of 2017.
The Republic of Ireland under-21 international has become a key figure in Eddie Howe’s side and was voted by supporters as the player of the month for December and January.
The 23-year-old has made 27 appearances in all competitions and scored his first Championship goal in the win over Yeovil Town on Boxing Day.
The former Everton trainee joined the club in the summer of 2012 from Torquay United and was an important part of the side that won promotion from League One last season.
Injuries disrupted O’Kane’s start to the current campaign, but he impressed on his return to the starting line-up, including an eye-catching display against Liverpool in the FA Cup.