The 29-year-old spent two years on the staff at Old Trafford before a spell at local rivals Manchester City.
He made his professional debut during a loan spell at Swindon and since then his clubs have included Millwall, Rochdale and Walsall.
Grimes played against Southport last season, one of 17 appearances for National League rivals Barrow.
Southport have signed former Manchester United academy midfielder Ashley Grimes for next season.