Motherwell's Fir Park will host the Irn-Bru Scottish Challenge Cup final on Saturday, 25 March.
The match, which will be shown live on BBC Alba, has a 12:30 GMT kick-off.
Dundee United overcame Queen of the South 3-2 in Saturday's semi-final and St Mirren came from behind to beat The New Saints 4-1 on Sunday.
TNS were one of two Welsh sides to feature in this year's competition, with two from Northern Ireland also taking part.
Next season, League of Ireland sides Sligo Rovers and Bray Wanderers will play in the cup tournament, which is run by the Scottish Professional Football League and involving teams from the Scottish Championship, League One and League Two.
United have never won the Challenge Cup but fellow Championship side St Mirren took the trophy in 2005.
"We're delighted to make today's announcement that Fir Park will stage this season's Irn-Bru Cup Final, including making tickets available to fans from as little as £5," said SPFL chief executive Neil Doncaster.
"We wish both clubs the very best of luck for the final and hope they produce a classic for supporters in the stadium and those watching live on BBC Alba."