Great news for the future of the club and the 17-year-old was unable to hide his delight at the news.
"I'm over the moon to have signed the contract;" said O'Keefe who joined Southend two-years ago from Ipswich Town.
"It is what I have always wanted to do, ever since I started playing football at the age of nine. It is a real dream come true. I never thought that it would happen this quickly, even though I spent nearly all of pre-season with the first team."
O'Keefe, who can play centrally or on the wing, impressed in last week's FA Cup defeat against Brentford. He scored twice and took the tie to extra time with a screaming free-kick from long range.
That impressed the watching Steve Tilson but it was actually after a reserve team game at Wycombe Wanderers in September that the youngster discovered he was being lined up for his first professional deal.
"After that the gaffer, Steve Tilson, approached me and everything has now been completed which is great," said O'Keefe. "I'm really pleased and now the aim is to work as hard as I can to get better."
Another of O'Keefe's target is to also work his way into the first-team. He has already been on the bench four times this season and hopes to figure in Tuesday's FA Cup replay with AFC Telford at Roots Hall.
"My main target now is to get into the first team," he said. "I just want to get on that pitch - it has got to be the best feeling in the world. We did well to get back into the game at AFC Telford with Jean-Francois Christophe getting a late equaliser, even though it didn't really happen for us. I'm looking forward to the replay now and maybe even getting on."