Okumu was elected to the parliament in 2001 on the ticket of the Forum for Democratic Change until 2016 election when he quit the party to run for parliament as an independent candidate and won. His election was challenged in court by FDC candidate Christopher Acire who alleged irregularities in the electoral process.[3] The case ended in favour of Okumu who served out his term in the parliament. He lost his parliamentary seat in the 2021 election for the first time since 1996. He was sacked from the parliament by National Resistance Movement (NRM) candidate Simon Wokorach who scored about 14,000 votes to Okumu's 2,200 votes.[4][5]
In April 2005 he was arrested together with Michael Nyeko Ocula for the suspected murder of Alfred Bongomin. Later they were acquitted. It is suspected the charges were fabricated to eliminate opposition politicians, similar to what happened to Muhammad Ssegirinya and Allan Ssewanyana.[6]