Ms Malkin secured the Wakefield Council seat with a majority of 456 votes.
She will replace Paula Sherriff who stepped down after she became the MP for Dewsbury earlier this year.
There was a 15.83 per cent turnout for the by-election.
The results in full:
Lorna Victoria Malkin (Labour) - 909 votes
Nathan Garbutt (UKIP) - 453 votes
Anthony David Hill (Conservatives) - 299 votes
Lucy Victoria Brown (Yorkshire First) - 124 votes
Daniel Woodlock (Liberal Democrats) - 86 votes
Daniel Krstan Dearden (TUSC) - 24 votes