T-Mobile has already lined up a successor to Munro, with Unilever Bestfoods senior category marketing manager Philip Chapman set to replace him in January.
A T-Mobile spokeswoman said that it was discussing other career opportunities with Munro.
Munro joined T-Mobile in 1994 and was promoted to marketing director two years ago. He had previously headed its consumer insight, research, analysis and pricing strategy.
His resignation follows accusations that T-Mobile's UK brand advertising has lost its way. The German firm is reviewing its global brand strategy, which will include the closure of its Hammersmith office, as first revealed by Marketing (3 November).