Mascarenhas was born in London to Malik Mascarenhas and his wife, Pauline (née de Croos), both from the Bharatha community of Sri Lanka. He grew up in Perth, Australia and attended school at Trinity College, Perth; other alumni include Australian international cricketers Simon Katich, Tim Zoehrer, and Craig Serjeant. In 1996 Mascarenhas returned to England to pursue a professional cricket career.

Early Cricket

Mascarenhas had great success in Australian junior cricket, captaining Western Australia at Under-17 and Under-19 state level competition.

Domestic career

County Cricket

Returning to England, he played a single Minor Counties Championship fixture for Dorset against Cornwall, taking 7/64 in his only match for the county. During the same season he joined Hampshire, where he continued in excellent form, with 6–88 on debut (the best figures for a Hampshire debutant since Teddy Wynyard made 6–63 in August 1899). He then proceeded to make the first Rose Bowl century against Worcestershire in 2001. In 2004, he was the first player to record a hat trick in Twenty20 cricket, claiming the wickets of Mark Davis, Mushtaq Ahmed and Jason Lewry of Sussex. He was part of the Hampshire team that won the C&G Trophy in 2005 and to finish runners-up in the Frizzell County Championship. In 2006, it was announced that Mascarenhas would receive a benefit year during the 2007 season as a reward for his excellent all round play for the county.

Following Shane Warne's retirement at the end of the 2007 season, Mascarenhas was made club captain for the 2008 County Championship season. During the 2009 County Championship Mascarenhas missed the first matches of the season while playing in the IPL with the Rajasthan Royals. On his return he led Hampshire to the final of the 2009 Friends Provident Trophy at Lord's, where Hampshire beat local rivals Sussex by 6 wickets.

Prior to the 2010 County Championship, Mascarenhas played for the Rajasthan Royals in the IPL, during which he picked up an ankle injury. Still injured for the first part of the 2010 English county season, Mascarenhas returned for Hampshire in the Friends Provident t20 against Kent, but during the match the injury flared up once more, therefore ruling him out for the rest of the season.

During the 2013 season he announced, aged 35, that he would be retiring from county cricket at the conclusion of the campaign, bowing out after 18 seasons wi