The 35-year-old announced his retirement as a Hampshire player on the county's website on Tuesday afternoon, although the wording of it did not suggest a terminal end to his playing days.
Mascarenhas has earned a reputation as a limited-overs specialist - he made 20 ODI and 14 Twenty20 appearances for England - and he may choose to carry on as a freelance player in the shorter forms of the game.
He will not play again for Hampshire, though, with his 18-year association with them ended by an Achilles problem.
"It's been the toughest decision of my life to call time on my career at Hampshire. I feel I have so much left, but my Achilles just isn't up to it and, as a result, I have to retire," said Mascarenhas, whose exploits earned him a deal with Rajasthan in 2008.
"I have had an amazing time here for 18 seasons; there have been many highs and lows, but one thing that has stayed constant is the guys I have played with. All have been tremendous talents and, more importantly, top blokes."
The Australia-raised all-rounder scored the first century at Hampshire's home the Ageas Bowl and took the first recorded hat-trick in T20 cricket in a spell of five for 14 against Sussex in 2004.
Further distinction followed in one-day cricket. He hit Yuvraj Singh for five sixes in an over in 2007 and that remains an England record, while he captained Hampshire to the T20 title in both 2010 and 2012.
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