McManus will still not be able to play in September’s LV= Insurance County Championship clash against his former employers though.
The 27-year-old will be available for all other games, and has signed a two-year deal that will see him stay at Wantage Road until at least the end of 2024.
“I’m delighted to sign on a permanent basis for Northamptonshire.” said McManus.
“I’ve loved my time here so far this season and it’s a great club.
"I’m thoroughly enjoying playing alongside the lads and working with the coaching staff.
“I’m really excited about the next two years with Northamptonshire and to see where we can go and to challenge for silverware.”
Poole-born McManus is a Hampshire lad and was quick to take to Twitter to thanks the south coast club for all they have done for him in his career.
"After 10 amazing years at Hampshire CCC, firstly lon the academy and then progressing into the first team playing squad it is time for a new challenge and a new chapter in my career," he wrote.
"I would like to sincerely thank the staff, players and fans for the support and friendships I have developed and will continue to have in the future.
"As a boy who followed the club growing up, it was a privilege to play for them and I am grateful for the friendships and memories I have made there.
"Making my debut in 2015 and winning the Royal London One Day Cup are moments in my career that will live long in the memory.
"I wish everyone at Hampshire CCC all the best for the future."