Manuel Uribe, who once weighed half a ton, left his house on Wednesday for the first time in five years.
Six people pushed Uribe's wheel-equipped iron bed out to the street, as a mariachi band played and a crowd gathered to see the man who once weighed 560 kilograms (1,235 pounds).
"It's nice (referring to being outside). Many thanks to my travelling Mariachis (traditional Mexican guitarist)," Uribe said after taking a sip from a champagne bottle.
Unable to leave his bed for more than five years, Uribe has lost 180 kilograms (397 pounds) since he began a high-protein diet a year ago. He now weighs about 380 kilograms (840 pounds).
To celebrate the milestone, a forklift lifted Uribe's bed onto a trailer pulled by a pickup truck and the 41-year-old mechanic rode through the streets of San Nicolas de los Garza, a Monterrey suburb.
Dozens of reporters and photographers followed Uribe as he passed the town's plaza and church, waving at clusters of people eager to get a glimpse of him.
"I'm very proud of him and very happy. I hope God continues to give him the strength to move forward," Uribe's neighbour, Leonor Garza said.
Uribe was a chubby kid, weighing more than 115 kilograms (250 pounds) as an adolescent.
In 1992, he said his weight began to balloon further.
Since the summer of 2002, Uribe has been bedridden, relying on his mother and friends to feed and clean him.
He drew worldwide attention when he pleaded for help on national television in January 2006.
Afterwards, an Italian and a Spanish doctor both visited and offered him gastric bypass surgery.
But Uribe chose to accept help from Mexican nutritionists working with the Zone diet which he says he will stick to until he reaches his goal weight of 120 kilograms (265 pounds).
Doctors say it may take between three and four years for Uribe to reach his goal.
Uribe said he plans to start a foundation to help overweight people get medical assistance and teach them about healthy eating habits.