The Democratic Party has reserved a seat for unionist Lau Chin-shek to contest in September's Legco election.
Only three members of the party's Kowloon West office had shown an interest in the four Kowloon West seats.
District office head Chan Ka-wai said the party reached an agreement to let Mr Lau, whose membership has been suspended for almost a year, run on a joint ticket in the geographical poll.
Mr Lau will run with James To Kun-sun under the joint banner of the Democratic Party and Confederation of Trade Unions, of which Mr Lau is chairman.
The unionist was suspended after he refused to quit The Frontier, which the Democrats consider a separate party.
Democratic Party chairman Martin Lee Chu-ming and vice-chairman Yeung Sum were approved to stand in the Hong Kong Island geographical constituency.
