The 62-year-old Wales international boss, who spent five years in charge of the club between 2006-11, returned earlier this year to work alongside head coach Chris Chester and coaching assistant Lee Gilmour.
And the former France and England coach, who left part-time outfit Batley at the end of last season having helped them reach the Qualifiers, has played a part in Trinity securing a place in the top eight for the Super 8s phase of this Super League campaign.
And, on agreeing to extend his stay for 2018, Kear told the club's website: "I have got great affection for the club as most people will know from my first stint here.
"I have enjoyed working with [chairman] Michael Carter, Chris and the coaching staff this season, so I am really looking forward to next year.
"It is great to see how much we have improved on last season but we still have plenty to do over the next six weeks."