Ousted legislator Emily Lau Wai-hing will renounce her British citizenship to take part in the geographical polls in May.
Ms Lau, a leading member of The Frontier, will submit her application for an SAR passport today. She will stand in New Territories East.
Ms Lau has to forfeit her passport because the Government has restricted foreigners to 12 specified functional seats.
The Basic Law says foreign passport holders cannot take up more than 12 of the 60 legislative council seats.
Christine Loh Kung-wai of the Citizens Party has already given up her British passport. Dr Huang Chen-ya of the Democratic Party is not joining the election because he does not want to give up Australian citizenship.
Ms Lau said last night that it had taken her months to announce the forfeiture of her passport because she had not wanted to yield to the government requirement too easily.