Left-arm seamer Amir, who returned to the test arena this year following his suspension, will be available for Essex from June 19.
"We are thrilled that Mohammad has decided to join us for half of the 2017 campaign," Essex head coach Chris Silverwood told the club's website.
"He is still only young but has proved himself at international level already, so it is a real coup to get this signing completed."
Amir, 24, was rated as one of the world's most exciting young bowlers when he burst on to the scene as an 18-year-old before he became embroiled in a spot-fixing scandal in 2010.
He was one of three Pakistan players jailed in November 2011 having admitted that he had deliberately bowled a no-ball in the fourth test against England at Lord's.
Amir served three months in jail and was banned from all forms of the game until January 2015 when he was cleared to play domestic cricket in Pakistan.
His international suspension was lifted this year and he played four tests against England, taking 12 wickets.
Amir has taken 69 wickets in 20 tests.
(Reporting by Martyn Herman, editing by Ed Osmond)
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