The 29-year-old, who also won the world title last year, posted a total time of 2min 34.62sec after one downhill and one slalom run.
"I can't quite believe it. This is really overwhelming. My confidence was a bit knocked before I went down, especially because the downhill didn't go great this morning," said the German, who had looked unusually jittery in the start gate.
She finished ahead of Austria's Nicole Hosp at 0.40sec and US favourite Julia Mancuso, who made a key mistake halfway through the course to finish third at 0.53sec despite leading after the downhill.
Höfl-Riesch was fifth after the morning's run, but put in a smooth performance in the slalom – her speciality – to take her third Olympic gold medal after combined and slalom wins in Vancouver in 2010.
Slovenia's Tina Maze, last year's overwhelming World Cup winner, finished fifth.
"My slalom wasn't good, I didn't start well, I was trying to find the right feeling and I didn't manage that," she said.
"I'm not as confident as I was last year in the slalom. I'm trying to do something more this season and it's not working out."
The 30-year-old double world champion has been battling back after a disappointing start to the season and missed the podium by 10 hundredths of a second.
"It's hard to be fourth. I'm not skiing bad, but still I'm not winning and I'm not the last one.
"It's like something in the middle, I didn't have the best season, but I'm still skiing well so I have some podiums and I'm happy about that."
Switzerland's Lara Gut was second after the downhill and a favourite for the podium but made an expensive mistake halfway down the floodlit course and skied out.
She was one of nine racers who failed to finish the tricky run, including Austrian former double world champion Elisabeth Görgl, Sweden's Lotte Smiseth Sejersted and Switzerland's Dominique Gisin.
"It hurts, but I know that's sports," said 22-year-old Gut, who was taking part in her first Olympics.
"I knew that other girls like Maria (Höfl-Riesch) and Nicole (Hosp) were strong in slalom so I had to take every risk. I made a mistake and it was over.
"It seems you will win the super-combined if you're a good slalom skier," added the speed specialist.
"If I want to be on the podium again for super combined, I have to work on my slalom."
Canada's Marie-Michele Gagnon, winner of the sole World Cup super-combined race this season, fell forward after catching a gate with her ski, and appeared injured, holding her left arm as she got up.
For 30-year-old Hosp, who missed the last Olympics due to injury, this was a second medal after slalom silver in 2006.
The former overall World Cup winner, who also took world bronze in the discipline last year, led a pack of strong Austrians including Görgl, Michaela Kirchgasser and 2011 super-combined world champion Anna Fenninger.
But the latter two had to make do with a seventh and eighth place.
In all, 31 racers tackled the slalom course which was new to many, after braving an icy and challenging 2,700-metre downhill in the morning.
The super-combined tests racers' ability to tackle both speed and technical courses but it is the event least featured at World Cup level, with just two or three races per year.