According to him, a decent and responsible government should be based on honesty, integrity and mutual respect.
Lewis added that he "must leave the government as he no longer believes these values are respected."
He also said that he sent a letter of resignation to British Prime Minister Boris Johnson.
Earlier, British Welsh Secretary Simon Hart announced his resignation.
On July 5, British Chancellor of the Exchequer Rishi Sunak and his counterpart Health Minister Sajid Javid stepped down from their posts.
After that, five more ministers left the government and called on Boris Johnson to resign.
Johnson, in turn, said that Cabinet members should not quit during a crisis.