Grant became CEO in 2003 and will leave following the close of the deal, along with other senior executives including Chief Financial Officer Pierre Courduroux and Chief Technology Officer Robert Fraley, Monsanto said on Monday.
German conglomerate Bayer is preparing to close its $62.5 billion (46.1 billion pounds) takeover of Monsanto this quarter, giving it control of more than 25 percent of the world's seed and pesticides market.
Condon, the head of its Crop Science division, will stay in that role after the Monsanto deal is wrapped up, Bayer said.
Monsanto's Chief Operating Officer Brett Begemann will assume the same role at Bayer's enlarged Crop Science division, and will be based in St. Louis.
Bayer has been divesting assets to win over antitrust regulators for its proposed takeover.
Grant said he has "made the decision to pursue new opportunities following the closing" of the deal but did not give any further details.
(Reporting by Anirban Paul in Bengaluru and Ludwig Burger in Frankfurt; Editing by Sai Sachin Ravikumar/Shailesh Kuber/Alexander Smith)
