Lamberti, a veteran of the South African business community, was appointed to the Eskom board by President Cyril Ramaphosa as part of a push to reform state companies after years of corruption allegations under Jacob Zuma.
In a letter addressed to Pravin Gordhan, minister of public enterprises, Lamberti said "while mistakes were made," there had been no findings in the judgment of race or gender discrimination against him.
"Despite this, there has been a mainstream and social media frenzy of generally inaccurate commentary," he said. "This is being fueled by a political agenda and legally incorrect interpretations of the judgment, which have culminated inter alia in the most vitriolic defamation of my person."
A spokesperson in Gordhan's office said Saturday the minister didn't try to persuade Lamberti to stay and the resignation had been accepted.
Lamberti last week apologised for comments made to former employee Adila Chowan after a court found him guilty of impairing her dignity when he referred to her as "female employment-equity" in front of fellow managers. Lamberti said he "apologises unreservedly" for the remarks to Chowan, an Asian woman.