The engineer, James Damore, wrote his opinion in a memo he sent last week. The document – which also criticized Google's diversity efforts – was later published online.
Damore confirmed his dismissal in an email to news organizations. He said the company acted against him because he was "perpetuating gender stereotypes."
Google Chief Executive Officer Sundar Pichai sent a note to all company employees about the memo. He said reaction within the company had resulted in "a very difficult time."
He said the company strongly supports the right of all employees to express their opinions. But he noted that parts of Damore's memo had violated company policy by "advancing harmful gender stereotypes in our workplace."
"To suggest a group of our colleagues have traits that make them less biologically suited to that work is offensive and not OK," Pichai wrote in his message.
He added that the memo had affected many Google employees, "some of whom are hurting and feel judged based on their gender."
Damore accused Google of having a bias on the political left. He said this had created "a politically correct" culture that prevented honest discussion of diversity.
He also attacked the idea that gender diversity should be a company goal. "The distribution of preferences and abilities of men and women differ in part due to biological causes," he wrote in the memo. "These differences may explain why we don't see equal representation of women in tech and leadership."
Damore said he filed a case with the U.S. National Labor Relations Board accusing Google of trying to shame him into silence. He said he was also exploring possible legal action.
On Tuesday, Damore received support and a job offer from Julian Assange of WikiLeaks.
"Censorship is for losers," Assange wrote on Twitter. "Women & men deserve respect. That includes not firing them for politely expressing ideas but rather arguing back."
Publicity over the memo comes as the American technology industry has battled accusations of sexism and discrimination.
The U.S. Department of Labor is currently investigating whether Google pays women less than men. The head of Uber recently lost his job after the ride-sharing company was accused of widespread sexual harassment and discrimination.
I'm Bryan Lynn.