The Hull FC loose forward, 29, has linked up with Chris Chester’s side on a two-year deal.
Pontefract-born Westerman began his career at Castleford Tigers where he was named Super League Young Player of the Year in 2007 and has gone on to be one of the competitions’s leading ball-handling forwards.
He has had two spells at Hull FC and also featured with Warrington Wolves as well as an ill-fated short stint at Toronto Wolfpack.
On his move to Trinity, Westerman said: “I’m really looking forward to it.
“It was a big decision and I thought Wakefield was the right club to join.
“I know a few of the lads here. I played with Joe (Arundel) at Cas, Reece Lyne at Hull and I’ve also played with Broughy earlier on in my career.
“I’m looking forward to being part of this squad.
“I was happy with my form in 2019.
“I had a few little niggles at the start of the year but then I got plenty of games under my belt.
“For next year, I’m looking to build on that.”
Westerman earned his solitary England cap during the 2014 Four Nations but showed glimpses of his best at times with Hull this season.
He is Wakefield’s first confirmed signing for 2020 and head coach Chris Chester said: “To get someone of Joe Westerman’s quality at the club, on a two-year deal, is great news.
“Joe was in some great form for Hull FC in 2019 and I’m delighted he’ll be in the Red, White & Blue for the next two seasons.
“He’ll add a different dimension to our pack next season; I’m really pleased we’ve managed to secure his signature and I look forward to working with him.”
Elsewhere, London Broncos head coach Danny Ward has reiterated his commitment to the club following their relegation from Super League by signing a new two-year contract.
The former Leeds Rhinos prop forward, who joined the Broncos as a player in 2008, guided them to promotion from the Championship in his first season as head coach and took their survival fight to the last day of the season, when they suffered relegation on points difference.
Ward defied most expectations by guiding the Londoners to 10 wins from their 29 matches and his achievements were recognised with his appointment as an assistant to Great Britain coach Wayne Bennett ahead of the end-of-season tour down under.
Ward said: “I’m very happy to extend my contract with Broncos and a big thanks to the gaffer, David Hughes, for putting faith in me again. London is our home and I am truly privileged to coach RL in the greatest city in the world... what a job! It has been an incredible journey so far, suffering incredible highs and lows along the way, with a fantastic bunch of players and performance staff.”
London chairman Hughes said: “Danny is almost a Londoner now and has done incredible things with the squad here.
“You can tell by the way the boys play they have a huge respect for him and he’s instilled a togetherness that’s second to none.
“I am delighted he has decided to stay here for another two years and have every confidence that he and his backroom team will be working harder than ever to get us back to Super League as soon as possible.”
Castleford have made two changes to their 19-man squad for tomorrow’s elimination play-off at Salford Red Devils.
Loose forward Nathan Massey is back in contention after a shoulder injury and winger Greg Eden returns after a lay-off as they replace Mike McMeeken – who remains sidelined with a dead leg – and Callum Turner.
St Helens and Scotland prop Luke Douglas has retired aged 33.
The former Cronulla and Gold Coast front-row spent this season on loan at Leigh Centurions.
Saints have also announced the departure of second-row Liam Cooper, 22, who has been on loan to Halifax.
Sheffield Eagles winger Ben Blackmore has rejoined Featherstone Rovers on a two-year deal after originally leaving in 2015.