He was born in the Welega Province west of Addis Ababa and he headed to the capital in 2005 to pursue a running career after winning some regional races. Merga made his international debut in 2006, winning the Paris Half Marathon in a time of 60:45. Later that year, he finished sixth at the 2006 IAAF World Road Running Championships, helping Ethiopia to a bronze medal in the team competition. In December that year he won the Montferland Run 15 km race in a course record time of 42:48. He took the half marathon gold medal at the 2007 All-Africa Games but just missed out on a medal at the 2007 IAAF World Road Running Championships, finishing in fourth place.