Rose, who was signed by Keith Curle shortly after Cobblers won promotion to League One in 2020, scored seven goals in 85 appearances across two seasons at Northampton but became a bit-part player under Jon Brady, mainly used off the bench.
He was released by Brady as part of the retained list last week but will remain in League Two after being snapped up by Boro boss Steve Evans. He joins Carl Piergianni, Michael Bostwick and Aaron Chapman in a busy start to the summer at Stevenage.
“I am delighted to get it over the line," said Rose. “As soon as the season finished, the move was something I wanted to make happen and now I can’t wait to get started.
“I have worked with the gaffer before at Mansfield, I know what he’s about and I played the best football of my career under him. I scored a lot of goals for his team, and hopefully I can do it again this season at Stevenage.”