The 23-year-old has linked up with the Pilgrims after United concluded an agreement with county neighbours Gainsborough Trinity to complete Walker's transfer of registration.
Walker, who played under Craig Elliott at Shaw Lane last season, scored four goals in 19 appearances for the Pilgrims in 2014-2015 and made a further nine outings during the 2015-2016 campaign.
He has also since played for Buxton.