The 21-year-old winger, who bagged a hat-trick in Friday's 52-0 win over Castleford Tigers, is now tied down to the South Yorkshire club until the end of the 2017 season.
"I'm very pleased to be offered a new contract and I can just focus on improving as much as possible now," he told the club's official website.
"I've enjoyed my time here so far, it's gone really quickly but Hull are an ambitious club with a very ambitious owner and good management and staff.
"The fans are very passionate too so it's the place I wanted to stay and a club I wanted to commit my future to. I didn't think twice about moving on, I just wanted to stay here and I'm looking forward to the next four years."
Lineham moved to the KC Stadium in 2011, following a two-year spell with York City Knights.