The Indonesian businessman, whose company International Sports Capital have acquired 70 per cent of Inter, was officially named president on Friday with former incumbent Massimo Moratti taking the role of honorary president.
Thohir will head an eight-man board of directors at San Siro, including business partners Rosan Roeslani and Handy Soetedjo, while Angelomario Moratti, Massimo's son, will serve as vice-president.
The 43-year-old believes he has the "passion" to bring success to the club, and has praised the work done by Mazzarri this season.
"Inter is a winning team," Thohir said. "It is beautiful and exciting to see a financially healthy club at international level. The world of football is changing, the Financial Fair Play is one aspect (of that).
"Our goal is to make this club stronger. I, Handy and Rosan promise to work hard with Massimo Moratti, Mazzarri and with the team.
"During these (past) months important bases have been laid for Inter's future thanks to Mr Mazzarri. Over the next two to three years it will be a great challenge for us to make this team even more competitive.
"There is confidence in what Mazzarri does; the goal is to make sure that Inter are increasingly winning.
"I want to mention a pillar of Inter, (former president) Giacinto Facchetti, who said 'the secret of all triumph is the strength of their conviction'. Our belief is our passion to pave the way for the success of Inter."
Massimo Moratti added: "I am truly pleased I have found new owners of this glorious club. I am convinced they are more than equipped to keep on adding new successes to our beloved colours.
"Personally I feel honoured I have been the president of Inter for so many years."
Inter have amassed 25 points from 12 league games and currently lie fourth in the Serie A table.
