He stepped into the water in Nakhon Phanom province at 10.19am before reaching Khammouane province in Laos over one and a half hours later at about noon.
The daring “One Man and the River” charity stunt is raising funds for hospitals on either side of the Mekong — Khammouane Hospital in Laos and Nakhon Phanom Hospital in Thailand.
Donations exceeded 41 million baht shortly after Tono touched down on the Lao side of the river at midday, according to organisers.
The star was accompanied on his mission by dozens of local swimmers and former athletes, all under the close watch of emergency teams in boats and kayaks.
Thousands of Lao locals lined the riverbank to greet Tono as he emerged from the river. The Thai celebrity towelled off and took part in a ceremony at a local temple before heading to greet a welcome committee at Khammouane Hospital.
He will swim the return leg to Thailand this afternoon and expects to complete his quest by reaching Nakhon Phanom at about 4.30pm.
Tono is also swimming against a tide of criticism, with detractors condemning him for “making merit with other people’s money” while others blame him for “burdening” rescuers by undertaking the swim.
The haters weighed in with negative comments on social media even as the swim was livestreaming on Saturday.
His supporters said much of the criticism was politically motivated, after Tono had resisted calls to take sides during last year’s crackdown on anti-establishment protesters. Some said his critics were attacking Tono and his project to gain free publicity for their cause.