Sebastian Coe was elected president of the International Association of Athletics Federations (IAAF) after beating Ukraine's Sergey Bubka by 115 votes to 92 in a ballot of the governing body's 50th Congress.
The Briton takes over as head of a sport battling a public relations crisis with the IAAF accused of failing in its duty to address doping amid allegations that blood doping was rife in athletics.
The former Olympic 1,500 metres champion will replace Senegalese Lamine Diack, who has run the body for the last 16 years, at the end of the August 22-30 world championships in Beijing.
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"For most of us in this room, we would conclude the birth of our children are the biggest moments in our lives," said Coe, whose initial term will be for four years.
"I have to say given the opportunity to work with all of you in the future of our sport, is probably the second biggest and momentous occasion in my life."
Former Olympic pole vault champion Bubka congratulated Coe on his victory and was later elected one of four IAAF vice presidents.
Coe has aggressively defended the IAAF's record on doping over the last three weeks, saying the organisation had "led the way" on out-of-competition testing and laboratories, and introduced blood passports in 2009 to help weed out the cheats.
Coe has previously said that under his leadership the sport would move towards setting up its own anti-doping agency.