"Today is a truly special day in my life," Thohir said. "I am honored that Mr. Moratti has entrusted me with the responsibility to lead Inter into the next chapter, and I am excited to have him continue in the future as my partner. The job done by the Moratti family, from Angelo's great Inter to Massimo's treble record, has made Inter one of the most respected clubs in the world."
Thohir has also served as vice president of the Indonesian Olympic Committee and as Indonesia's chief of mission for the 2012 London Olympics.
"I am an entrepreneur but first of all I am a supporter and a sports lover," Thohir said. "I cannot wait to put our passion and international experience at the service of this fantastic club and its supporters."
It remains unclear if the 68-year-old Moratti, who has owned the club since 1995, will remain president.
"That I don't know," Moratti said outside the office of his family oil company, Saras.
"Every president leaves his mark," Moratti added. "The important thing is that he's always respectful of the rest of the world, beyond his own job, and I think these people also have that in mind. ... They're people that really mean well and are good character-wise, too."
Inter and city rival AC Milan have each won 18 Serie A titles, second on the all-time list behind Juventus' record 29. Inter has also won three European Cups.
Moratti took over the club after his father Angelo was owner during the team's early glory years in the 1960s, when Inter won the European Cup twice.
After some difficult years under the younger Moratti, Inter returned to the top after the 2006 match-fixing scandal and won five consecutive Serie A titles from 2006-2010. In 2010, Inter also won the Champions League and the Italian Cup for an unprecedented treble in Italy, with Jose Mourinho as manager.
However, Inter struggled again in the past two seasons finishing sixth in 2012 and ninth last season with the same number of losses (16) as wins.
Inter is coming off its first loss of this season, a 3-0 defeat to first-place Roma, which left the team in fourth place under first-year manager Walter Mazzarri. The Nerazzurri visit Torino on Sunday.