The 39-year old Kolkata GM scored 6.5 points from 7 rounds to take the top prize ahead of Sethuraman (5.5 points) and French Woman Grandmaster Vera Nebolsina (5.5 points).
Ganguly remained unbeaten through the seven rounds, securing six wins and drawing one game with Alexandra Kosteniuk.
Played my first ever Fischer random tournament and won @BielFestival. #Champion #Biel #Switzerland #Chess… https://t.co/QoWwtKVeVP
— Surya Sekhar Ganguly (@suryachess64) 1657613308000
His wins came against Arashavir Musaelyan (Switzerland) Sai Kalluri Hari Charan (India), Robin Angst (Switzerland), Jose Antonio Herrera Reyes (Spain), Sethuraman and Konstantinos Ragios (Greece).
Sethuraman had to settle for second place as a defeat to Ganguly hurt his chances.
Meanwhile, teenage Indian GM D Gukesh will be in action in the Rapid event as part of the Grandmaster Triathlon and the eight-player classical event for GMs. He finished sixth with 3.5 points in the ACCENTUS Chess 960 event on Sunday.
The eight-player GM field includes Vincent Keymer (Germany), UAE’s Salem Saleh, American veteran Gata Kamsky and China’s Yu Yangi among others.