By Ben Hirschler

LONDON (Reuters) - GlaxoSmithKline has struck a deal for Luke Miels to start as its new head of pharmaceuticals in September, following a lengthy dispute over his contract with his former employer AstraZeneca.

Britain's biggest drugmaker poached Miels in January in the first major appointment by incoming GSK Chief Executive Emma Walmsley. But his arrival was stalled by an AstraZeneca lawsuit disputing when he could join.

GSK said on Monday it had now struck an agreement with AstraZeneca for Miels to start on Sept. 4, avoiding the need for a court case over his contract.

Miels had headed AstraZeneca's European business and his defection was a blow to the company, which has seen a number of senior management departures.

For Walmsley, his appointment is viewed as pivotal, since he will be a key lieutenant as she tries to steer GSK's core pharmaceuticals business towards improved productivity and higher profits.

Originally, GSK had hoped for a lengthy handover period during which Miels would work alongside outgoing pharma head Abbas Hussain. However, the delay in his arrival means this will not now be possible.

Miels, who has both commercial and scientific experience after working at AstraZeneca, Roche and Sanofi, will arrive as GSK is looking to a new wave of drugs to offset the decline of lung treatment Advair.

Walmsley, who became GSK CEO on April 1, worked in marketing and management at L'Oreal for 17 years before joining the drugmaker and has her roots a long way from the pharmaceutical lab bench.

That has raised doubts among some investors about her insight into prescription drugs and she is expected to rely heavily on advice from Miels, as well as GSK's research boss Patrick Vallance.

(Editing by Kate Kelland and Alexander Smith)