He was a farmer and a chairman of the Gaelic Athletic Association[citation needed].
O'Neill was elected Member of Parliament for the Mid Ulster constituency in 1951 as an Independent Nationalist, serving in the House of Commons.
He retired at the 1955 general election and the Mid Ulster seat was narrowly won by Tom Mitchell of Sinn Féin.
At the 1956 Mid Ulster by-election the League stood O'Neill in an attempt to unseat the abstentionist Mitchell, but this split the nationalist vote and independent Unionist George Forrest was elected.
This article about a member of Parliament representing a Northern Irish constituency is a stub.