Born in Athy, County Kildare, Ryan's political interest arises from his involvement in the 1970s and 80s with The Simon Community, an organisation which works with and for homeless people.
He was first elected in 1981 to the 16th Seanad by graduates of the National University of Ireland in 1981, defeating Professor Augustine Martin. His election was welcomed by an editorial in The Irish Times as "one of the best deeds in a naughty world". The paper noted that "the graduates of the National University of Ireland, the privileged as many would see them, the people who have had the inestimable gift of university education, gave their vote to a man who had devoted his life wholeheartedly to the Simon Community — Mr. Brendan Ryan".
He was a member of the Senate from 1981 until his defat at the 1993 election to the 20th Seanad. He was re-elected to the 1997 to the 21st Seanad, and was a member until he lost his seat in 2007.
Ryan is a lecturer in Chemical Engineering at the Cork Institute of Technology. In 1995 he wrote "Keeping Us In The Dark", a book concerning censorship of freedom of information in Ireland. He also writes a weekly column for the Evening Echo newspaper.
Ryan is a fluent speaker of the Irish language. In May 2006, he introduced the Genealogy & Heraldry Bill 2006  in Seanad Éireann which aimed to provide a sound legislative basis for the State's delivery of heraldic services.
He lost his seat in the 2007 election to Seanad Éireann.