Morrison put pen to paper on an extension that ties him to Reading until 2016.
The 21-year-old told the club's official website: "It's always nice to sign a new deal, now I've got to push on and show all the Reading fans what I can do.
"I'm improving every day and I think if the manager was to call upon me I'd be ready. Since I've been here the gaffer has given me his backing, I know he and the coaching staff believe in me which gives me a load of confidence."
Reading manager Brian McDermott also believes that Morrison has a bright future at the Madjeski Stadium.
"Sean is a player who went out on loan and did really well for us he's got the tools to work at his game and be a really good centre half," he said.
"If he keeps working and keeps doing what he's doing he'll be a very, very good defender. I'm sure he will be."
Morrison earned a number of admires while on loan at Huddersfield Town last season, helping the Yorkshire club earn promotion to the Championship.