The Wanaka-based athlete raced around the 42.2km off-road course from Lake Hawea to Glendhu Bay in a time of 3hr 31min 57sec to finish more than 18min clear of second-placed Nigel Seidelin.
First woman home was Esther Sanson, who was third overall with a time of 3hr 54min 15sec.
The race was held in perfect conditions, although temperatures climbed to about 28degC by the time competitors made it to the finish line.
"It was definitely the hottest race conditions I've run in so far this year," Lawrence said.
Wanaka doctor Andrew McLeod was the third male to finish in a time of 4hr 12min 43sec.
The marathon was the first race in the 7 in 7 event, being undertaken by Aucklander Mal Law to run 360km through the Queenstown Lakes this week, as part of a fundraising campaign for the New Zealand Blood and Leukemia Foundation.
Race director Matt Tuck said about 70 people had entered the race, spread across the full and half marathon distances.
Law finished 16th overall in the marathon with a time of 5hr 15min 20sec.
The half-marathon was won by Chris Langston in a time of 2hr 01min 07sec, followed home by first female Sania Smit in 2hr 03min 01sec, with former All Black Marc Ellis third in 2hr 04min 41sec.
