Russian Olympic Committee president Alexander Zhukov was also among the nine candidates elected to the IOC on the final day of its general assembly in Buenos Aires.
Zhukov made it by a vote of 63-29, with two abstentions. The 29 votes against was the most received by the nine candidates, a possible sign of Russia's contentious relations with the West.
Among the other new members are former Olympic high jump champion Stefan Holm of Sweden and Kenyan running great Paul Tergat.
The elections took place before the IOC election of a new president to succeed Jacques Rogge. The new members were being sworn in later Tuesday and were not eligible to vote.
DeFrantz, a former IOC vice president, was running for election later to the policy-making executive board. The U.S. has been without a member on the board since Easton lost his seat in February 2006.
Without a voice at the top IOC table and holding few top jobs in international sports, the U.S. had lost considerable clout over the years in the Olympic movement underlined by New York's defeat in the race for the 2012 Olympics and Chicago's first-round elimination in the vote for the 2016 Games.
Under Probst and CEO Scott Blackmun, the USOC has made significant strides in mending fences with the IOC and establishing an international presence. Last year, the USOC and IOC resolved a long-standing dispute over Olympic revenues that had kept the American body alienated from the rest of the world.
Probst's election comes as the USOC weighs a possible bid for the 2024 Summer Games. The U.S. hasn't hosted a Summer Games since 1996 in Atlanta or the Winter Games since 2002 in Salt Lake City.
Probst and Zhukov were elected to the IOC based on their positions as national Olympic committee presidents. Six others made it as "individual" members and Holm as an athlete.
With Tuesday's elections, the IOC now has 112 members.
The U.S. and Russia now each have four members. Britain also has four, while Switzerland has the most with five.
Holm, who won the high jump at the 2004 Athens Games, was elected by a count of 81-10. Tergat, a five-time world cross-country champion who won the silver medal in the 10,000 meters at the 2000 Sydney Olympics, had the biggest voting support of all the candidates 86-9.
Also elected Tuesday: KLM executive Camiel Eurlings of the Netherlands, Mikaela Maria Antonia Cojuangco-Jaworski of the Philippines, Bernard Rajzman of Brazil, Octavian Morariu of Romania and Dagmawit Girmay Berhane of Ethiopia.
Eurlings replaces King Willem-Alexander of the Netherlands, who resigned his IOC position after acceding to the Dutch throne in April.
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