Pudit Kittithradilok, 34, admitted running a Ponzi scheme whereby he promised investors artificially high financial returns.
About 40,000 people were persuaded to pour more than $160m (£120m) into his companies.
The court found he engaged in illicit lending and some 2,653 counts of fraud. Thanks to his confession, it halved his sentence to 6,637 years and six months.
He is unlikely to serve more than 20 years, as Thai law sets a maximum 10-year term for each of the two crimes he was convicted of.
Prosecutors told the court that Pudit organised seminars where attendees were encouraged to invest in what he said were businesses linked to property development, beauty, used cars and exports, among other things.
According to the Bangkok Post, investors were promised generous returns, plus incentives to bring new members on board.
As with any pyramid scheme, these new cash injections would then be used to pay off the earlier backers.
Pudit had been held in Bangkok Remand Prison since his arrest in August, when he was denied bail.
The court fined his two companies the equivalent of $20m each. Pudit and the firms were ordered to repay around $17m to the 2,653 identified victims, with 7.5% yearly interest. (Courtesy BBC)