For more than three and a half decades, Engelhorn led the pharmaceutical companies Boehringer Mannheim and DePuy Inc. In 1997 he sold the two firms (in which together he had a 40% stake) to Hoffmann-La Roche for more than $10 billion.
Since late 2013, there have been ongoing investigations by the German authorities concerning suspected tax frauds between Engelhorn and his daughters, avoiding capital transfer taxes of up to Euro 440 million (US$475 million). As of January 2016, the family's lawyers conceded capital transfer tax evasions in the amount of Euro 135 million (US $145 million) to the court.
As of June 2015, according to Forbes, Engelhorn had a net worth of $6.2 billion. He died on 13 October 2016, aged 90.