Mary Lockhart, a Labour activist for 30 years and former member of the party's Scottish executive, said independence "won't deliver Utopia.
"But it will deliver the chance for socialists to help shape a Scotland which reflects the identity of its people."
Writing in a personal capacity in a Sunday paper, Ms Lockhart – who chairs the Scottish Co-operative Party – said she was disillusioned with Labour's efforts to take on the Tories at Westminster and found it "offensive" the party was campaigning alongside the Coalition parties in Better Together, the pro-UK group.
A spokesman for Yes Scotland said: "More Labour voters will vote Yes as they realise Westminster isn't working for them. They know independence offers the opportunity for a fairer Scotland."