Soderberg led his nearest challenger Calum Hill by eight shots heading into the overnight session but was unable to continue his strong form, sitting at 21 under after three rounds.
Grant started the day at 10 under, but she birdied six of the first 10 holes before chipping in from just off the green on the final hole to set her clubhouse target at 17 under, three shots behind Soderberg with six holes to play.
Soderberg then bogeyed the 13th and 15th holes, made pars on the 16th and 17th holes, and was one shot ahead when he teeed off on the 18th. He hit a nice tee shot, but his shot went into a bunker on the edge of the green.
The 33-year-old chipped out and his par putt was too short, but his bogey shot circled the hole and stayed on the ground, leaving him with double bogey and a five-over 77, finishing third after just five tee shots.
As Grant prepared for a possible play-off, news of her sixth Ladies European Tour title reached the practice field.
“It’s a lot of mixed emotions,” Grant said.
“Like I said before, I feel really bad for Sebastian right now. I can't even put it into words. I can't imagine how he feels. At the same time, I'm amazed to be here again as a champion, in my hometown. It's just amazing.”
The result broke several records, as no player had ever led by eight shots after 54 holes on the DP World Tour and yet failed to win, while Grant's 11-shot deficit was the largest ever to be overcome, surpassing the 10-shot comebacks of Paul Lawrie (1999 British Open) and Jamie Spence (1992 Canon European Masters).
Soderberg and Scotsman Hill were tied for second at 16 under, while Sweden's Johanna Gustafsson and Britain's Alex Fitzpatrick and Andy Sullivan were tied for fourth at 13 under.
