The 19-year-old Victorian has played nine matches in his first two seasons at the club after being recruited with pick 16 in the 2011 NAB AFL Draft from the Calder Cannons.
He debuted in round 23 last season against Melbourne, his only match in 2012, before playing eight of the past nine matches in 2013.
Sheridan gathered a career-high 23 touches in round 21 against Melbourne at the MCG and kicked a career-best two goals against Port Adelaide on Saturday night.
Dockers coach Ross Lyon said he was really pleased with the progression of Sheridan after his performance against Port Adelaide.
"He's been strong. He's grown," Lyon said.
"Credit to our development academy. They're producing the goods with the players.
"I'm lucky as senior coach that they can help produce really good players.
"Tommy signed during the week, he's in and he's happy."
