Danny Cahill, a 40-year-old land surveyor and musician from Broken Arrow, Okla., lost 239 pounds (108kg) to win the $250,000 grand prize.
Cahill went from 430 pounds (195kg) to 191 pounds (86kg), losing 55.58% of his body weight in six months and three weeks - and breaking the record for the most weight lost by any contestant.
The Nielsen Co. said that with 13.4 million viewers, the season eight finale of The Biggest Loser on Tuesday night had the show's biggest audience in four years.
Erik Chopin, who won in 2006, held the previous record, dropping 214 pounds (97kg). He went from 407 pounds (185kg) to 193 pounds (87kg).
In an interview Wednesday on the Today show, Cahill said his family motivated him to change his lifestyle.
NBC said season nine will premiere January 5.
