The Scottish Green Party has launched its campaign in the Glasgow North-East Westminster by-election.
Its candidate, David Doherty, said a win for his party could "deliver greater progress on the environment".
The seat was vacated by former Speaker, Michael Martin, who resigned amid the ongoing MPs expenses row.
Meanwhile, the leader of the Scottish Senior Citizens Unity Party, John Swinburne, will no longer stand in the election to be held on 12 November.
He has withdrawn from the vote due to unforeseen circumstances.
Mr Doherty launched his campaign at the Lambhill Stables project - an initiative to bring a 150-year-old stable complex in the north of the city into public use.
He said: "The Green influence in the Scottish Parliament has resulted in initiatives like the Climate Challenge Fund, which is helping to support this innovative local project.
"A foot in the door at Westminster would deliver even greater progress on the environment and social justice. Westminster is crying out for a Green voice.
"Both the UK and the Scottish governments have failed to bring about the transformation we need, so I'm proud to be here to support a community that's getting the job done for itself."
Mr Doherty was joined at the campaign launch by Patrick Harvie, the party's co-convenor and MSP for Glasgow.
"The Greens are the only party to understand that Glasgow's economic problems can't be fixed by refloating the same failed economic model, and we're also the only party in this election with a clear policy to end the benefits trap," he said.
"We'll be campaigning positively in this by-election, with policies which offer real opportunities to people in Glasgow North-East."