The IWF says Ajan beat Antonio Urso, the Italian leader of European weightlifting, 86-61 in a vote of member federations. Seven candidates had entered the contest.
Hungarian official Ajan has led the Budapest-based IWF since 2000. He was previously its CEO-like secretary general for 25 years.
Weightlifting's longstanding doping problem was shown with 49 of the 111 positive tests, most involving steroids, in reanalysis of samples from the 2008 Beijing Olympics and 2012 London Olympics.
Ajan was an IOC member for 10 years until 2010, and remains an honorary member.
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