Mindshare takes over the business from Walker Media, which has handled the bulk of the account since 2000.
Mindshare has also been appointed to the digital media planning and buying business, some of which was held by Profero.
A spokeswoman for M&S confirmed a review was taking place but declined to comment further at this stage.
It is understood that the review was prompted by M&S's desire to focus on a digital and multi-channel approach to media.
The move ends months of speculation about M&S's marketing arrangements, after Patrick Bousquet-Chavanne took over as marketing director in February, following the retirement of Steven Sharp.
There is not currently a review of M&S's creative advertising business, which is held by Rainey Kelly Campbell Roalfe/Y&R.
The news comes as M&S revealed its trading results for the fourth quarter of 2013, which showed clothing sales were up 0.6 per cent on a like-for-like basis, suggesting a turnaround after they declined for the last ten quarters.
M&S's chief executive Marc Bolland said today that he was aiming to transform the company into an "international, multi-channel retailer."
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