Scottish Labour leader Wendy Alexander will not be prosecuted over failing to register donations, the Crown Office has confirmed.
Ms Alexander was reported by the standards commissioner
The Holyrood watchdog referred her to the procurator fiscal for not recording gifts to her leadership campaign in the MSPs' register of interests.
Prosecutors recommended the issue be dealt with by the Scottish Parliament's standards committee.
The SNP claimed Ms Alexander's position was still "far from secure".
The case will be handed back to the Scottish Parliament's standards commissioner, Jim Dyer, who initially sent it to prosecutors because of his requirement to refer alleged rule breaches which may be an offence.
Ms Alexander has since updated her register with details of 10 donors who each gave about £1,000 to her leadership campaign.
The Paisley North MSP said she was initially told she did not need to register the donations, after seeking advice from the clerk to the standards committee.
Dr Dyer - who operates independently from the committee - later said this was "incorrect", prompting Ms Alexander to make a voluntary registration.
In a statement, the Crown Office said: "After very full and careful consideration of the report from the Scottish parliamentary standards commissioner, crown counsel has concluded that a prosecution would not be appropriate in the full circumstances of this case."
Prosecutors said, in reaching their decision, there was a degree of uncertainty surrounding interpretation of the rules, that Ms Alexander had sought advice and that a voluntary disclosure was made.
A spokesman for the Scottish Labour leader said: "The Crown Office has found that not only would a prosecution not be in the public interest but it would not be appropriate as Ms Alexander has made clear all along she took written advice from the standards clerk and made a voluntary disclosure to parliament."
Nationalist MSP Roseanna Cunningham said the decision would surprise nobody, adding: "Following the Electoral Commission's failure to take action, it was unlikely the procurator fiscal would do anything else."
The Crown Office ruling came after an earlier decision by the Electoral Commission not to report Ms Alexander to prosecutors after her leadership campaign received an illegal £950 donation from Jersey-based developer Paul Green, because he is not a UK-registered voter.