The 2018 Super League Young Player of the Year will now remain with the club until the end of the 2022 season after signing new terms.
Trueman signed a three-year extension at the start of this season but after a fantastic campaign has been further rewarded.
Trueman, 19, was set to make his England Knights debut on the current tour of Papua New Guinea but had to pull out due to the injury that, crucially, also saw him miss Castleford’s Super League semi-final loss at Wigan Warriors.
“I’m very happy to get this new deal over the line,” he said.
“I now have my future for the next four years all sorted so I can now just focus on my rugby.
“When the offer got put in front of me I just could not turn the chance to extend my stay even longer here at Castleford.
“I got my opportunity this year because of a couple of injuries but my focus now is getting back into the team in 2019, we have some talented halfbacks in the team so competition for places is high.”