A goal from Foster gave Boro a 48th minute victory over Chasetown in front of a crowd of 3,111 at Liberty Way in the Play-Off Final.
They will join Leamington FC who were promoted as Champions and Rugby Town who avoided relegation to stay in the division.
In League One, Mk Dons, Leeds, Milwall and Scunthorpe will contest the play-offs whilst Northampton and Crewe were relegated into League Two.
Exeter and Wycombe were promoted whilst Chester City dropped out of the Football League after a 2-1 home defeat by Darlington.
In the Midland Combination Premier Division, Southam lost 1-0 at Walsall Wood but Nuneaton Griff won 3-1 at Brocton whilst Massey Ferguson drew 3-3 at Meir KA