"She's back," wrote Red Bull, the skier's sponsor, on Instagram, posting a video in which the 40-year-old former Olympic and world champion smiled: "I hear St Moritz is nice this time of year."
Vonn left the sport in February 2019 following a series of major injuries but she has been free of pain since a right knee replacement in April.
"So I have some news, my body is finally put back together," Vonn said.
"One thing I realise is life is really short and if you have an opportunity you have to take it. There's nothing I love more than ski racing."
Vonn was the most decorated women's skier with 82 World Cup victories when she retired. Her mark has since been eclipsed by fellow American Mikaela Shiffrin's 99.
She requested a "wild card" entry to compete in two super-G races at St. Moritz, Switzerland on December 21 and 22, taking advantage of a new invitation system that allows former stars to return to the elite circuit after years away from competition and to have better starting positions.
"She says if she had known earlier about the benefits of this operation, she would have done it a long time ago and would never have stopped her career," French skier Alexis Pinturault said on Thursday.
Along with Vonn, alpine skiing this season also saw the return of another legend in October in the form of Marcel Hirscher.
The Austrian, now competing for the Netherlands, however seriously injured his knee in early December and ended his season -- and his second career -- after only three races.
'Not an easy path'
Vonn "has knees that are much more damaged than Marcel's were and it ended very badly for him," observed 2021 overall World Cup winner Pinturault.
"Obviously I wish her the best and I hope that she will manage to do something very interesting for herself and for the sport, but her path is not easy," he added.
"I'm happy that she can do what she loves the most again," said Italian Sofia Goggia, a former Olympic downhill champion, and speed event specialist like Vonn.
"I'm also a little worried about her, because she's someone I love very much and we do a dangerous sport."
Last week, Vonn took part in two super-Gs in a lower-level competition at Copper Mountain in the United States and finished 19th and 24th, just over two seconds behind the winner each time.
"It was a success. Some say I was slow but I think it was great," she said.
Before returning to competition in Switzerland, the American will be the opener this weekend at the World Cup in Beaver Creek, where a downhill and a super-G are taking place.
She recorded her first World Cup victory in 2004 and won three Olympic medals -- including downhill gold in 2010 in Vancouver.
Vonn also won 20 World Cup titles, including four overall crystal globes, eight world championship medals and secured 137 World Cup podiums.
The next Winter Olympics take place in Milan and Cortina d'Ampezzo in 2026.
