Afridi, Pakistan's captain for the forthcoming World Twenty20 in India, will be available for the whole Blast tournament, Hampshire said.
Nicknamed 'Boom Boom' for his aggressive approach with the bat, Afridi is also an effective leg-spin bowler.
The value of his bowling was evident in last season's final when, playing for Northamptonshire, he took three for 14 although that could not prevent a Lancashire win.
Afridi, who has had spells with several counties, last played for south coast club Hampshire in 2011 when he took 17 wickets in 10 matches and thumped 80 off 42 balls in the semi-final defeat to Somerset.
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Afridi, who has played 27 Tests, 398 one-day internationals and 90 T20s for Pakistan, has largely become a Twenty20 specialist in recent times. He holds the record for most Twenty20 international wickets with 91.
"This year it has been a challenge to get the top players over for significant periods of the Blast so we are delighted that he is available for the entire tournament," said Hampshire director of cricket Giles White.