Mergia was born in Showa province, and moved to Addis Ababa in his youth. He had grown up on traditional Oromo, Amhara and Tigrinya songbook melodies, and taught himself the accordion age 14. His mastering of the accordion, as well as the keyboard and his talent for "re-purposing folk songs into funkier modern melodies," defined his contribution to popular music in Ethiopia. In the 1970s, Hailu Mergia was the keyboardist in the Walias Band, a jazz and funk band with a hard polyrhythmic funk sound influenced by western artists like King Curtis, Junior Walker and Maceo Parker. In the period, it was harder for working bands in the region to make a living, after Mengistu's Derg government imposed breaks to Addis Ababa's nightlife, but music was still being regularly recorded, and cassettes were the typical release format, given they were easy to duplicate and distribute. Walias Band had a 10-year long residency at Addis's Hilton hotel in this period. Due to the Derg dictatorship, censorship was often a problem for the area's musicians, but Mergia acknowledged one way around censorship was to only create instrumentals. He later noted: "When you sing or write lyrics you have to support the government, and if you don’t do that then you have a problem." Ethiopian music was typically led by a vocalist, and fewer than five instrumental albums were released during the 'golden age' of Addis' music, one of which by was one of Mergia's landmark albums with the Walias Band, Tche Belew. As a side project, Mergia joined the Dhalak Band around this period and recorded the cassette-only Wede Harer Guzo with them, a jazz-infused album with a dominance of improvisation. Mergia's organ work for the band was one of the Walias Band's key characteristics, but during a 1980s tour of the United States, Mergia and several other members decided to stay in the US, effectively ending the band's career, although their legacy in Ethiopia was strong by this point, especially via their 1977 instrumental "Muziqawi Silt." It was only several years after moving to the US that Mergia recorded a new album, Hailu Mergia & His Classical Instrument, in 1985, during which point he was playing with the Zula Band. Hailu recorded the album alone in a small studio belonging to an acquaintance that Mergia met at Howard University, where he had begun studying music. He stopped performing in 1991 and opened a restaurant. Since 1998 Mergia has worked as a taxi driver, mostly based around Washington DC's Dulles Airport. “Hailu Mergia & His Classical Instrument", was re-released in 2013 on the Awesome Tapes From Africa label. Two years later, his first new record in over two decades, "Lala Belu" was released, with Mergia accompanied by Mike Majkowski and Tony Buck. This was followed in 2020 by a full-band album, "Yene Mircha".
