Mayer, 42, has a two-year-old son, and announced her pregnancy with twins last week.
In recent years, Yahoo! has struggled to build upon its core search business in a meaningful way.
Unlike Google, it has not ventured into ambitious projects like Street View or Android, and it has failed to make money from people that find themselves on its web pages.
Galloway made the comments on Bloomberg TV
And due to the complex nature of its business, the core search function has at times been quite literally worthless.
Yet under Mayer's leadership the Yahoo! business as a whole has improved its fortunes. Its share price is now around double what it was when she arrived at the tech giant in 2012.
Professor Galloway claimed his frustration was borne out of Yahoo!’s inability to monetise “the most trafficked website in the world."
Galloway said: “I realise how awful this sounds, but she got a reprieve from death row because she’s pregnant with twins.
“She is going to go down as the most overpaid CEO in history.
“She’s coming up to being due about a quarter of a billion dollars."
Yahoo! is attempting to spin off Alibaba - which continues to be valued more than the core search business. Alibaba sells wholesale goods between businesses and took £7.7bn in revenues last year.
On Tuesday, US tax authorities denied Yahoo!'s request to spin off Alibaba in a tax-free transaction.
In September, Mayer updated the Stock Market with her pregnancy news but felt the need to reassure investors she would return to work after just two weeks away.
HuffPost UK has reached out to Yahoo! and New York University's Stern Business School for comment and this article will be updated with their response.
Meanwhile, reaction Galloway's comments has been scathing.