Wendy Alexander has announced her resignation as leader of the Scottish Labour Party.
The embattled leader said she was standing down with "deep regret".
The announcement comes after Holyrood's Standards Committee ruled she should be suspended from Parliament for one day for failing to declare on donations to her leadership campaign.
Ms Alexander said the row over the donations had become a "distraction" from the real issues facing Scotland.
She said she was the victim of a "partisan" decision by the Standards Committee and claimed there had been a "breach of natural justice".
Ms Alexander's departure now presents Labour with the prospect of a leadership contest in Scotland.
She announced her resignation in a statement delivered before TV cameras at Scottish Labour headquarters in Glasgow.
Her voice still hoarse from a throat infection, and on the day after her 45th birthday, Ms Alexander announced her decision to resign following the decisions this week of Holyrood's Standards Committee.
Ms Alexander said: "I hope the events of recent days will lead to reflections by all MSPs and parliament officials on the appropriateness, objectivity and effectiveness of our current procedures.
"I acted in good faith and the written advice of parliamentary authorities. I believe there has been a breach of natural justice in a partisan decision," said Ms Alexander.
