Starmer explained that allowing Burnham to run for a Westminster seat would 'divert our resources' from Labour's campaigns in the upcoming May elections.
Labour's National Executive Committee (NEC), including Starmer, voted to deny Burnham permission to stand in the Gorton and Denton by-election.
Starmer highlighted the importance of focusing all resources on existing crucial elections across England, Wales, and Scotland.
The decision was based on the need to avoid unnecessary elections that would draw focus and resources away from essential campaigns.