Ngozi Okonjo-Iweala was frontrunner for the role until the Trump administration last October said it wanted another woman, South Korea’s Yoo Myung-hee.
Yoo has now withdrawn her candidacy.
If confirmed in the role, Dr Okonjo-Iweala would be the first woman and the first African to lead the WTO.
Dr Okonjo-Iweala on Friday praised her rival for the post and said: “There is vital work ahead to do together.”
A WTO nominations committee in October recommended its 164 members appoint Dr Okonjo-Iweala as a replacement to outgoing chief Roberto Azevedo; a spokesman at the time said all had approved the appointment “except for one”.
President Donald Trump – who had described the WTO as “horrible” and biased towards China – wanted Yoo, South Korea’s trade minister.
Yoo said her decision to withdraw her candidacy was made in “close consultation” with the US. She said: “South Korea will actively contribute to reaching consensus for the next WTO chief and co-operate with her and participate in the WTO reform process.”
The White House congratulated Yoo on her “strong campaign” for the position and for being a “traiblazer” as South Korea’s first female trade minister.
In a statement, it said the “US stands ready to engage in the next phase of the WTO process for reaching a consensus decision on the WTO director general”.