The midfielder has agreed a two-year contract after the two clubs settled on a compensation package.
Morsy was a free agent after turning down the offer of a new deal but the Burslem club were entitled to a fee for the former Wolves trainee as he is under the age of 24.
"He's a very tenacious central midfielder who can handle the ball and drive forward," said Chesterfield boss Paul Cook. "He's got that little bit of devilment in him that we'll need to curb at times but good players have that.
"He's a good age and he comes in with a desire to get better. When we found out that he may be available, we moved heaven and earth to get him here."
Morsy, 21, admitted Cook was a key factor in his decision to move to the Proact Stadium.
"I know the ambition of the club and I want to be a part of it," he said. "I've known the manager for a number of years and I know his philosophy. That was a big factor in my decision to sign."
Morsy, who spent nine years in the Wolves academy before being released as a 16-year-old, initially joined Vale's youth set-up before being handed a professional contract in 2010.
He made 32 appearances last season, helping Micky Adams' side win promotion to League One. In total, he scored four goals in 78 appearances during his spell at Vale Park.
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