Mr Pichai, who is also the boss of Google's parent company Alphabet, said on X/Twitter he was "unbelievably saddened" and Ms Wojcicki was "as core to the history of Google as anyone".
Once described as the "most important Googler you've never heard of", Ms Wojcicki was present at the company's beginnings when, in 1998, she rented out her Menlo Park garage to the search engine firm's founders, Sergey Brin and Larry Page.
She was later persuaded to leave her job at chip giant Intel to join Google, becoming the firm's 16th employee.
