Campaigner and lawyer Mike Dailly, who had served as a vocal Labour activist in Glasgow since the 1990s and had previously subscribed to the Better Together camp in the run up to the Scottish independence referendum, turned heads three years ago when he announced his defection to the SNP.
Last year it was confirmed Mr Dailly had been appointed by First Minister Nicola Sturgeon to help lead her party's Social Justice and Fairness Commission.
But less than six months after taking up the post, Mr Dailly has announced his resignation from the commission, stating that he can no longer be associated with the "useless" think tank.
Writing on Twitter, Mr Dailly said: "I am resigning from @theSNP Social Justice Commission forthwith. My professional life has been about changing lives and using the law to tackle barriers to achieve fairness.
"The First Minister appointed me this body but it is useless. I cannot be associated with this."
He added: "If you are going to have a think tank. It needs to think. Have space, time and proper support to enable that."
The membership of the Social Justice and Fairness Commission was announced by the First Minister at the SNP's 2019 Spring Conference in an effort to build on the work of the Growth Commission and strengthen the case for a new independence referendum by tackling poverty and inequality.
Dundee City East MSP Shona Robison and the SNP's Westminster Social Justice spokesperson Neil Gray MP were installed as convener and deputy convener of the 19-strong team in October.
Mr Dailly, who is Principal Solicitor and Solicitor Advocate at Glasgow's Govan Law Centre, said he joined the SNP as a result of the UK voting to leave the European Union.
It is unclear whether Mr Dailly will remain a member of the Scottish National Party following his announcement that he is stepping down from the party's social justice commission.