Labour candidate Daniel Evans was elected as councillor for Rotherham's Thurcroft & Whiston ward in a by-election after intending to withdraw his candidacy but missing the deadline by hours.
Mr Evans had aimed to pull out after it was revealed he received a suspended prison sentence in 1988 for actual bodily harm and common assault. Although legally able to stand for election as his conviction was spent, Mr Evans had breached Labour Party rules by failing to declare his past during selection.
He took the ward with 323 votes, 51 more than his Liberal Democrat rival.
'I believe you may have seen recent press reports where I make clear why I think this is the right course of action for myself, for the council and for the Labour Party,' he told leader Mark Edgel (Lab).
A new by-election will be held after May's full council elections.