Barr, who was made redundant from her position as marketing director at John Lewis a year ago as part of wider management changes, will report into Rita Broe, group head of European marketing, and Hany Fam, general manager of MasterCard UK & Ireland.
Ben Rhodes, who heads up brand marketing at MasterCard UK & Ireland, and Andrew Miles, head of customer marketing, will report into Barr.
Fam said the appointment of Barr will help MasterCard's transformation into a wider payments brand, developing "more innovative customer propositions" and engaging with a "broader set of stakeholders" across the retail sector.
Barr said: "My priority will be to ensure that our marketing strategy helps deliver on the overall business objectives, driving even higher levels of consumer engagement with the brand."
Prior to joining John Lewis as its first board-level marketer in 2007, Barr held marketing roles at Woolworths, Superdrug, KPMG, Athena and Wickes.