Patrick joined the Tigers on loan from Huddersfield Giants in April with his deal with the Giants due to expire at the end of this season.
In 2016, the 27-year old managed 10 games for an injury-stricken Giants before being allowed to leave after being told his contract would not be extended.
Patrick made his Huddersfield debut in 2009, against Castleford Tigers, and has gone on to make over 100 appearances for the Giants.
Last year he spent the whole of the 2015 season on loan at Wigan Warriors in a move that saw Jack Hughes go the other way joining Huddersfield.
“I’m over the moon, it’s a great club to be at! I’ve enjoyed the last 5/6 weeks and I’m really looking forward to the next three years here,” Patrick said.
Tigers head coach Daryl Powell has been impressed with the forward in recent weeks.
“We are delighted to confirm Larne will be with us for the next three years. He is an experienced front rower who’s line speed in defence and ability to break the defensive line is outstanding,” he said.
“He has fitted in well while on loan and we feel he still has a lot of improvement in him.”
Tigers CEO Steve Gill said he was pleased to announce another quality player to be joining Castleford Tigers.
“Larne has impressed Daryl over the past few seasons, and we feel his best rugby is still ahead of him,” he said.