He will join from rival computer giant Oracle, which he has been with for seven years, most recently as vice-president and director of marketing.
Barley will report directly to Neil Holloway, Microsoft's UK managing director and EMEA vice-president, and gains a seat on the executive management team.
He is to oversee the 90- strong marketing team, which includes the 12-strong corporate affairs and press office units, and the work of the four PR agencies used by Microsoft in the UK.
These are August.One Communications for technology, Edelman PR Worldwide for corporate, The Red Consultancy for consumer work including promotion of the X-box and, finally, Weber Shandwick for the mobility division, which includes pocket PCs.
Barley, who joins next month, replaces Oliver Roll, who has become MD of marketing in Asia-Pacific and is now based in Hong Kong.
As Roll has already taken up his new post, group marketing manager for tech professionals Julie Kerry will cover Barley's role in the interim.
Prior to joining Oracle, Barley worked for, among others, Hewlett-Packard and Bull Information Systems in a sales and marketing career in the tech sector spanning more than 20 years.
This week Microsoft looked set to take the first steps to complying with a ruling by US regulators to prevent anti-competitive behaviour.
It was reported this week that the company plans to reveal around 400 units of computer codes and previously secret internal operating rules to allow computer makers to create machines with less dependence on Microsoft software. The US Justice Department is considering these concessions.