Mengistu was given numerous offers to play professionally for teams in Italy's Serie A and France, as well as Egypt's El Zamalek, but like earlier legend and coach Ydnekatchew, he refused all offers and stayed in Ethiopia wearing Saint George's characteristic "V" across his chest.

Mengistu wore the number 8 for the entirety of his club and national team career.

His international career began in 1958 and ended in 1970, following disappointment in the 7th African Nations cup in Sudan, where Ethiopia finished bottom of their group.

He did, however, coach the country to their first-ever CECAFA cup title in 1987, when the tournament was hosted by Ethiopia.

At the 2002 CECAFA Cup, Mengistu was honored before the tournament kickoff by the Council for East and Central Africa Football Association, along with five other east African footballers and three referees, including Tesfaye Gebreyesus, the Ethiopian who refereed at three ACN tournaments.