Born in Sheno, Oromia Region, his first major international competition was the 2007 World Championships in Osaka where he finished 11th in the heats. His first major win came at the 2008 World Indoor Championships in Valencia at the 1500 m, where he was initially disqualified for a lane violation after winning the race. However, the Ethiopian Athletics Federation made an appeal, and the disqualification was reversed, giving Mekonnen the gold medal. He came third in the Dream Mile at the Bislett Games in June with an Ethiopian record of 3:49.72 for the distance. He gained selection for the 2008 Beijing Olympics, but he just missed a place in the 1500 m final as he was eliminated in the semi-finals.