Barnes worked as a social worker before entering politics. An unsuccessful candidate in the 1969 provincial election, he was first elected to the British Columbia legislature in 1972, and re-elected five consecutive times, he served the people of British Columbia until 1996. Barnes and fellow NDPMLARosemary Brown were the first black politicians elected to a legislative office in British Columbia in the 20th century. He was particularly concerned with issues relating to social justice, human rights, and poverty.
Elected Speaker of the Legislature in 1994, Barnes was also the first black person to hold this position in any Canadian province.
The city of Vancouver has named a park after him in his memory, Emery Barnes Park at 1100 Seymour Street.
Barnes is buried in Robinson Memorial Park Cemetery, in Coquitlam, British Columbia. The headstone shows his full name as "Emery Oakland Barnes."
Constance Barnes, his daughter, was an elected member of the Vancouver Park Board and stood for the 2015 federal election with the NDP in the riding of Vancouver Centre.