THAI president Sumeth Damrongchaitham says the airline will operate the route to Sendai for Suvarnabhumi airport with three weekly flights per week.
The three weekly flights will use a Boeing 777-200, with 30 business seats and 279 economy ones, he said.
Mr Sumeth said earlier the service would begin in October this year.
Sendai, 300km northeast of Tokyo, will be the flag carrier's sixth destinations in Japan after Tokyo, Osaka, Nagoya, Fukuoka and Sapporo.
The addition will expand the airline's footprint in Japan, one of the most preferred destinations for Thai tourists and a high-potential market, he added.
THAI provided flights to Sendai for the first time in 2005 but scrapped it in 2014 due to losses and low demand.
