The club has activated an option to see the one-time England international remain at Wheldon Road.
Holmes, 28, has spent his entire career at Castleford and chalked up his 200th game for them earlier this season.
“Being at a club for such a long time shows a lot of loyalty from both sides - myself and the club,” said the tough-tackling forward who helped Tigers win the League Leaders’ Shield and reach a Grand Final in 2017.
“It is a great achievement and I am looking to build on it.
“It wasn’t my decision, the option was in the club’s favour and they notified me earlier on in the year they were going to take up that option.
“I’m obviously really glad they did so; I want to be here for next year and beyond.
“It is a starting point, so I’ve got next year to look forward to.
“Hopefully it will bring the best out of me and I can earn a longer contract.”
Castleford were riding high in second spot before the sport shut down in March.
However, since it resumed in August, they managed just two more wins in 11 games while a Covid outbreak meant they could not play their last fixtures and finished a disappointing eighth.
But Holmes is confident they can re-set for 2021.
“There’s a few lads coming into the last year of their contract and a few might retire at the end of next year,” he said.
“For them, there’s a lot riding on next year. On the flip side of that, we’ve had to play a couple of young lads who probably wouldn’t have got as much game time as they have and they’ve shown they can handle the pace and what it takes to play Super League.
“It has been a real bonus having those lads step up. They are gaining more confidence and feeling more comfortable around the lads and comfortable out on the field in a Super League game.”
Head coach Daryl Powell said: “Oliver has come through our system and you can see how much he loves the club; he works so hard and I think it’s demonstrated in his massive defensive efforts. He will do anything you ask him to do, whether it’s his favoured position in the back-row, or you ask him to go in the middle and he’ll go in there, tough as teak, and do what he needs to do.
“He carries the ball strong and is a really tough, resilient defender and I’m delighted he will be staying with Castleford and I’m looking forward to continuing to work with him. He has been an awesome player since I’ve been here at the club and his leadership is growing all the time.”
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