Shares of Bayer have dropped by roughly 25 percent since August 2018. That was the month that they lost their first lawsuit claiming that Roundup causes cancer. Bayer acquired Monsanto in a $63 billion takeover deal, and they've been fighting expensive lawsuits related to Roundup and other Monsanto products ever since.

In a statement, the 73-year-old chairman said that he felt they were making progress in dealing with the firm's legal woes and that it was therefore a good time for him to step down. He added that he had planned to step down last year when he turned 72, which is the board's recommended age limit, but he had been asked to stay on as the firm weathered a legal storm.

His successor has been named as Norbert Winkeljohann, a former head of the PricewaterhouseCoopers European audit firm who has been on the supervisory board of Bayer since 2018. He will step into the role after Bayer's annual shareholders meeting takes place on April 28.