Onanuga was born to the family of Anikilaya Ruling House in Ijebu Ode, Ogun State. He started his education at the Moslem Primary School, Ijebu-Ode, 1962–1969. He then went to Muslim College Ijebu Ode and finished in 1974 with a Grade One.

After briefly working for a year, he went to the Federal Government College, Odogbolu for his A-Level, between 1975 and 1977.

He was admitted to the University of Lagos in September 1977 to study Mass Communication. He graduated in 1980 with a second class upper.

Onanuga worked for Practions Partners in early 1982 and joined Ogun State Television as a pioneer staff in June 1982.

In July 1983, he moved to The Guardian in Lagos as a sub editor and left just 17 months after to start Weekly Titbits.

When the effort failed, Onanuga joined the National Concord in January 1985 as senior features writer. His service was later transferred to the African Concord magazine. Onanuga in 1989 was the international editor of the magazine, based in London. Later that year, he was appointed the editor.

But in April 1992, Onanuga resigned from Concord after he declined to apologise to the military dictator, General Ibrahim Babangida, over a cover story: Has Babangida Given Up? The story triggered the closure of the Concord Group by the junta.

Onanuga, together with Seye Kehinde, owner of City People Magazine, Dapo Olorunyomi publisher of Premium Times, Sani Kabir, who later became Sarki of Hausawa in Ebute Meta, Idowu Obasa, who served as chairman in Onigbongbo local government in Ikeja, Babafemi Ojudu senator in Ekiti and Kunle Ajibade teamed up to set up TheNews Magazine in February 1993.

After TheNEWS was shut down by the military government, the group floated TEMPO magazine and later P.M.NEWS in 1994.