Stevenson joins from EA Mobile, where she was product marketing director. Prior to that, she worked at T-Mobile International as head of MMS marketing.
Stevenson will be responsible for raising consumer awareness about the bookmaker's various mobile products and grow its marketing activity in the channel. She will report directly to Kristof Fahy, group marketing director at William Hill.
Her appointment comes as the brand invests in new technology to improve the mobile service. Last month, it unveiled a new version of its mobile optimised site, which gives users access to more than 500,000 markets every week.
It offers a number of iPhone apps including Shake-a-bet, Match Predictor and Mobile Sportsbook, and The Racing Post. It is also looking to integrate mobile cashless payments.
William Hill, which has more than 2,350 betting shops in the UK, has recorded a 23% growth in revenue coming from online, compared to a 2% growth in retail.