Voters in Park ward, Didcot, have picked a new town councillor following the resignation of Jerry Goff.
Eleanor Hards, representing the Labour Party, retained the seat on the Conservative-led Didcot Town Council with 378 votes.
She will replace Mr Goff, a Labour councillor and former mayor, who worked at JET Culham. He has now moved to France.
Mrs Hards, 56, a former mayor, South Oxfordshire District councillor for 12 years and chair of the district council, won the election by 44 votes.
Conservative Party candidate Michael Turner secured 334 votes and Liberal Democrat Anthony Worgan won 257 votes.
Mrs Hards said: "I am pleased, I worked hard for it. I was pleasantly surprised with the turn out, for a by-election I think it was reasonable."
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