Mattinson was fittingly the guest of honour at Sunday’s Ike Southward Memorial Trophy match after playing for both west Cumbrian clubs in a long rugby league career.
The number nine has been a key part of Town’s squad since signing for them from rivals Whitehaven in 2010 and Town admitted he would be a big miss.
Town chairman Garry Mounsey said: “Matty told us of his decision to retire from professional rugby at the end of last season.
"He has been a peerless player and leader for Town and has made over 100 appearances for the club.
“He will be greatly missed by all at the club and we wish him all the best for the future.”
The 31-year-old former Town skipper has suffered with injury problems over the last couple of years.
Originally a Wath Brow Hornets amateur, Mattinson turned professional with Whitehaven in 2005. He made over 100 appearances for the Recreation Ground side before his move to Workington.
Mattinson had won the National Conference Premier Division player-of-the-year award following his spectacular final season at Wath Brow.
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