Muirhead, who skipped Great Britain's women to gold at Beijing 2022, and Olympic silver medallist Lammie, booked their place in Saturday's gold medal game by defeating Germany's Klaudius Harsch and Pia-Lisa Scholl 8-3 in the first semi-final match on Friday (29 April).
The Swiss booked their spot after a tense extra end, beating Norway 8-7 in a thrilling later semi.
Norway trailed by 3 going into the final end, but scored exactly that to force the extra end. But their hopes were dashed as Switerland's Alina Paetz and Sven Michel held their nerve to reach the gold medal encounter. The two losing teams from the semi-finals will play-off for the bronze medal on Saturday.
Scotland overcome German challenge
The German duo advanced to the semi-final to meet Scotland after they bested Sweden 11-8 in a thrilling game play-off that was decided in an extra end.
But the third-place finishers from Group B could do little against an indomitable Scottish pair who are unbeaten in 10 games.
When Germany edged 2-1 up in the second end Muirhead and Lammie responded with a triple-score to re-take the lead 4-2.
The Scots then further dented their opponents' hopes in the fifth end when they stole two points to extend their lead out to 6-2.
Scholl was able to muster up a reply of one to close the gap but it did little to stem the Scottish tide. Muirhead and Lammie scored back one of their own in the sixth before then stealing another point in the seventh to take the score out to 8-3. Germany then chose to concede the game with one end remaining.
Victory over semi-finalists Germany marks what has been an impressive week so far for both Muirhead and Lammie who, in addition not to having yet lost all week, also have not given up a single steal.
Having previously won world and European titles, Muirhead is bidding for a rare quadruple in Geneva.
World Mixed Doubles Curling Champions: Friday results
Sweden 8-11 Germany
Canada 5-6 Norway
Spain 5-8 Korea
England 6-3 Spain
Germany 3-8 Scotland
Switzerland 8-7 Norway (after Extra End).
World Mixed Doubles Curling Championship updated schedule for Saturday (all time CEST, GMT+2):
Saturday 30 April
10:00 - Bronze Medal Game
14:00 - Gold Medal Game