Amir’s Essex stint appeared to be over after Friday’s T20 Blast game against Sussex Sharks, following the Pakistan Cricket Board (PCB) decision to recall its players.
However, the 25-year-old bowler has now been granted permission to return to Essex after undergoing fitness tests.
Essex, who are top of Division One, face Somerset on Aug 28.
The PCB had originally decided to revoke the NOCs given to 13 of its players playing in England and the Caribbean Premier League, ordering them to fly back by Aug 22.
The early recalls — because of the rescheduling of an upcoming World XI series — meant Amir, as well as Pakistan captain Sarfraz Ahmed (Yorkshire) and left-handed opener Fakhar Zaman, who was due to play for Somerset, had their county spells cut short.
But Amir, who took 10 wickets in a two-day victory over Yorkshire earlier this month, will now fly back from Pakistan on Aug 26 to play Somerset from Aug 28 to 31.
The left-armer will then return to Pakistan for the World XI series, which will be played in a window between Sept 10 and 16.
Essex, who have not won the title in 25 years, are 41 points clear of second-placed Lancashire in County Championship’s Division One with five matches remaining.