Born in Debre Birhan, Showa Province, Ethiopia, in 1946 to parents of Amhara and Oromo descent, Mergia grew up absorbing traditional Amhara, Tigrinya and Oromo songbook melodies. At the age of 10, Mergia and his mother settled in Addis Ababa.
At the age of 14 he started playing the accordion. He went to school in Addis Ababa and then joined the army music department. When he left the arm at the age of 16, he started his career as a singer and accordion player by fronting various touring groups around the country.  Mergia is known as a keyboardist, arranger, accordionist and bandleader. Mergia played with the Walias Band, an instrumental funk and jazz ensemble and fixture of the Addis Ababa hotel circuit.  Mergia and the Walias, Tche Belew released an LP album of instrumentals in 1977.
In 1981, Mergia and his Walias Band were part of the first ever US tour of an Ethiopian music group.They used this US tour to escape the dictatorial Mengistu Haile Mariam regime. Mariam was the President of Ethiopia between 1977 and 1991.  The US tour took two years. Mergia and some members of the Walias Band decided to remain in the US. Mergia settled first in Virginia before making Washington DC his permanent home. He is well known as a singing cab driver at the capital's Dulles Airport. Mergia, who has been playing his composed music privately, was rediscovered by the Awesome Tapes from Africa label, whose re-releases in the 2010s assisted him mount an effective late-career surge that resulted in the 2018 comeback album Lala Belu . Mergia plays live in the US with the New York based Afrobeat band, Low Mentality, and in Europe with two leading Australian improvisors.Tony Buck, and Mike Majkowski, who live in Berlin .