Baylay replaces Tim Davie who was promoted to director of audio and music last year. She was previously general manager of Microsoft online services division in the UK.
In her new role, Baylay will lead more than 400 staff responsible for marketing, communications, audience research and audience services across the BBC.
At Microsoft she had responsibility for the growth and development of the company's Windows Live and MSN businesses, including the recent acquisition of Multimap.
Baylay joined Microsoft in 1993, holding a range of marketing and management roles, running the international MSN businesses in EMEA, Asia Pacific, Greater China and the Americas before her most recent role.
Under Baylay's leadership, MSN was a founding member of the government-led co-operative effort to address the growing problem of cyberbullying.
Microsoft is also a member of the Home Office Task Force on Child Protection on the internet and Baylay was instrumental in ensuring that the good practice recommendations were reviewed and, in most cases, adopted by the business. She also oversaw MSN's participation in the Internet Watch Foundation.
Baylay began her professional career at Olivetti and Computacentre, working on IBM, Apple and Compaq. She is also a holder of a Diploma in Marketing from the Chartered Insitute of Marketing.