Around 185,000 children of unmarried mothers were adopted in England and Wales between 1949 and 1976.
Starmer's apology comes after a years-long struggle by affected mothers, adopted children and relatives.
"We deeply and sincerely apologize to the mothers who were told they were unfit and who were prevented from caring for their children," Starmer said in parliament, the BBC reported.
The shame is not yours. The shame has never been yours. The shame is ours.
Earlier in the day, Starmer met with activists ahead of the statement in the House of Commons.
