That decision comes a week after it emerged the Novartis subsidiary Novartis Investments S.A.R.L. paid $100,000 a month for 12 months to Essential Consultants, which is owned and controlled by Donald Trump's lawyer Michael Cohen.
Ehrat commented: 'Although the contract was legally in order, it was an error.
Ehrat said he hopes his departure will "bring the public debate on this matter to an end", but that might not happen any time soon.
The payments became public knowledge after Michael Avenatti, the lawyer for porn actress Stephanie Clifford, who is better known as Stormy Daniels, published details of an account used by Cohen to pay Clifford $130,000 so that she would keep quiet about her affair with the U.S. president.
In announcing his resignation, Ehrat, 60, stressed that while the deal was legal, it was a mistake.
In a statement, Novartis said that Felix R. Ehrat, the group general counsel, will be replaced by Shannon Thyme Klinger, who is now the company's top ethics officer, at the beginning of June. Novartis should have done more due diligence, he said.
After a much-publicized series of scandals and legal actions in Japan, Novartis has fielded bribery and kickback allegations in multiple countries-twice, in China's case-and paid at least two related fines: A $50 million penatly to South Korean authorities a year ago in a doctor kickbacks case and $25 million to the US government to settle charges of illegal doctor payments in China.
Daniels' attorney, Michael Avenatti, told NBC last week that Novartis was among several firms that paid large sums of money to a company controlled by Cohen.
Apart from AT&T and Novartis, Cohen was also paid by Korea Aerospace Industries and Columbus Nova, a NY investment firm whose biggest client is Renova Group, a conglomerate owned by US -sanctioned, Kremlin-backed Russian oligarch Victor Vekselberg. Jimenez left the company in September.
Jimenez told Bloomberg that Cohen had "oversold his abilities" in being able to explain the then-new Trump administration's position on healthcare issues. Rather than terminating the contract, Jimenez elected not to, because he anxious that ensuing litigation would cost more than paying out the contract would.
The case is under examination by the Greek and US authorities.
Novartis shareholders have urged Narasimhan to exert more "moral influence" over perceived ethical shortcomings that Jimenez in 2016 blamed on a "results-oriented" sales culture and some bad actors.