Arbroath 0-0 Dumbarton (agg 1-2)
Dumbarton will face Airdrie United in the promotion play-off final after a goalless draw away to Arbroath.
The Sons were 2-1 ahead after the first leg at Stratchclyde Homes Stadium against the side who finished second in Division Two.
They were indebted to keeper Stephen Grindley for preserving the lead.
Grindley pulled off a fine save to tip a curling 25-yard free-kick from Gavin Swankie around a post eight minutes into the second half.
And, moments later, he surpassed that with another superb stop to keep out Steven Doris' close-range header from Swankie's corner.
Swankie and Stuart Malcolm both fired wide as Arbroath laid siege to the Dumbarton goal, but they could not level the tie and face another season in Division Two.
Mark Gilhaney almost got on target for the visitors late on, but Darren Hill tipped his shot over.
With Airdrie, who finished six points behind the Sons, beating Ayr United to relegated the Division One side, the play-off final will feature the sides who finished third and fourth in the Second Division.
Arbroath: Hill, Baxter, Malcolm, Innes, McAnespie, Caddis (Kerr 87), Falkingham, Gibson, Sheerin (Samuel 74), Doris, Swankie. Subs Not Used: White, Birse, Busch.
Dumbarton: Grindlay, Kennedy, Lithgow, McNiff, Creaney, Wallace, Agnew, Nicoll, Gilhaney, Prunty (Graham 81), Dargo (Walker 64). Subs Not Used: Ewings, Gray, Lyden.
Ref: Craig Thomson