The Tigers made new offers to both players however the duo have decided to leave Wheldon Road at the end of the campaign.
Holmes is a product of Castleford's academy and made his debut for the club in 2010 at the age of 17.
“Castleford Tigers has been my entire adult life," said Holmes, who has made over 200 appearances in the colours of Castleford.
"It is all I have ever known since I left school and came through the Academy. All my life has been based around Cas, so to say that the club means a lot to me is a bit of an understatement.
“I wouldn’t change a thing about my time here. The people that I have met, the coaches that I have met, the fans, everything that has gone on during my time at the club has put me in the position that I am in today.”
Holmes is hoping to end his time with Castleford on a high as the Tigers prepare for next month's Challenge Cup final against St Helens.
If he features, it will be his second appearance in a Challenge Cup final, after he finished as a runner-up with Castleford in the 2014 showpiece with Leeds Rhinos.
He added: "I have played in the Challenge Cup Final in 2014 and at the time I thought I would have loads of chances to do it again, but it’s taken seven years to get back there. It is emotional and something I’m really proud of, but we still have one more game to go.
“Finishing on a high would be the best send off and to be able to do that would mean a lot to people, especially myself.”
Mata’utia joined the Tigers in July 2018 from Leigh Centurions and has gone on to become a beloved player for Castleford with his performances on the pitch and through his work in the local community.
“I’ve had a blast. This has probably been the best time I’ve had in my career being here at Cas," he added.
"It has made me love the game again and it gave me a different perspective of playing it for fun too.
“The first year I came here was probably one of the toughest times of my life and all those players who have been here since 2018 hold a special place in my heart. I’ve enjoyed every day been here at Cas and I’m pretty gutted to leave.”
Head coach Daryl Powell, who will also be leaving the club at the end of the campaign, added: “I don’t think you will see anyone who loves Castleford Tigers anymore than Oliver Holmes he was in tears talking about what it would mean to him to do something special with this year, and it was exactly the same when he was on the field after the semi-final.
“He is a 100 per cent man and has been class for Castleford during his time, and you will always get 100 per cent from him no matter what.
“Peter has been fantastic as a player, as a person and a leader, he has given everything in and out of the club within the community with food banks and other charitable causes.
"He has shown what he stands for as a man and he will be fully committed to making sure we achieve what we want to this season.”
Holmes and Mata'utia have not confirmed their next destination although both have been linked with a move to Warrington Wolves, who will be coached by Powell from next season.