Hasnain was banned from bowling international cricket after having his action reported during a Big Bash League stint with Sydney Thunder in January but that suspension has now been lifted
Ben McDermott, Mohammad Hasnain, Suzie Bates and Deepti Sharma are among the overseas wildcard picks selected for the second season of The Hundred.
Each of the eight men's and women's sides have added a fourth overseas player to their squads but will only be permitted to field three in a matchday XI.
Australia star McDermott - who has impressed in the T20 Blast for Hampshire Hawks, including with a 30-ball 83 against Middlesex - has been signed by London Spirit, while Pakistan fast bowler Hasnain will play for Oval Invincibles.
Hasnain was banned from bowling international cricket after having his action reported during a Big Bash League stint with Sydney Thunder in January but that suspension has now been lifted.
Other standout overseas picks by the men's sides include Birmingham Phoenix re-signing Imran Tahir - the veteran spinner took the competition's first hat-trick last season, against Welsh Fire - and Fire acquiring 17-year-old Afghanistan spinner Noor Ahmad.
The eight men's wildcard picks will each be paid £50,000, with the eight women's picks earning £15,000.
Men's teams will add a further player to their squads on July 7 through the domestic wildcard draft, which will come after the group stages of the Vitality Blast.
The women's teams have until the end of June to finalise their squads, with the complete lists to be submitted alongside the men's wildcard picks on July 7.
The men's competition begins on August 3 with a clash between defending champions Southern Brave and Welsh Fire.
In the main draft, Pakistan fast bowler Naseem Shah was picked by Welsh Fire while the Northern Superchargers drafted Wahab Riaz.