Clucas, 25, joined Hull from League One side Chesterfield in July 2015 for a reported £1.3m.
He scored six goals in 52 appearances in all competitions last season as Hull won promotion from the Championship.
"The spirit in the squad is second-to-none and we are determined to achieve our goals in the Premier League this season," Clucas told the club website.
Clucas played for the first time in the Premier League last Saturday as Hull beat champions Leicester City 2-1.

Isobel Parker, 23, who was known as Becky, died at a property in Booth Place, Burnham-on-Crouch, on 17 July.
Her mother described her as a "bubbly girl" and a "fantastic mother who adored spending time with her two precious children".
Matthew Smith, 23, of Wood Corner Caravan Park in Maldon, has been charged with murder.
He will next appear in court on 28 September.
A post-mortem examination found Miss Parker had been strangled with a ligature.
Her partner Shane said: "Becky was the best woman I could have ever wished to meet.
"We were so looking forward to the birth of our first child together, a little girl, who we were going to name Charmaine."
Midfielder Sam Clucas has signed a new three-year deal with Premier League side Hull City.
[NEXT_CONCEPT]
The family of a pregnant woman who was strangled to death in Essex said she was "an absolute angel".