Morsy, who was signed from Port Vale last summer, is now tied to the Spireites until the summer of 2016.
The 22-year-old midfielder is pleased to have put pen to paper. He said: "We had a great season collectively and individually I thought I did well so I'm delighted to have signed my contract.
"The manager showed belief in me, making me a mainstay in midfield and I knew exactly what he wanted me to do. When a manager believes in you that much, it is easy to repay. The fans also warmed to me straight away, which was a massive help."
Morsy is now looking forward to playing in a higher division following Chesterfield's Sky Bet League 2 title triumph. "We want a successful season in League 1," he said.
"We've got a very strong spine to the team, with a mixture of youth and experience and strengthening the squad will give us a very good chance next season. You saw what Rotherham did last season and if we strengthen I don't see why we can't have a really successful season."