At a central London hearing, a three-person panel ruled that a senior manager's comments about Julia Sommer were "sexist, demeaning, and derogatory."
At a work drinks, the manager made a joke about the size of her breasts and her sexual preferences, which the panel described as a "attempted joke gone horribly wrong."
"We concluded that the remark was a sexual one about the claimant's body," the panel said, adding that it would not have been made to a male colleague.
Although the manager called the claim "untrue and unfounded," the tribunal upheld complaints that he once told Sommer to "shut up" during a meeting.
According to testimony at the hearing, he criticized her "dominant" personality and plotted to force her out of her job under the guise that she was being laid off after going on maternity leave.
Sommer worked for Swiss Re Corporate Solutions in London as a political risk underwriter from 2017 to 2021.
The panel determined that she was unfairly dismissed and upheld her claims of direct sex discrimination, sex-related harassment, and maternity discrimination.
Compensation will be determined at a later date.
The 72-page ruling, dated August 12, was released on Wednesday.
In May, one of the few female CEOs of FTSE-100 companies, Amanda Blanc of British insurer Aviva, stated that misogyny was on the rise.
She spoke out after being confronted with sexist remarks from shareholders during the company's annual general meeting.
"I'd like to tell you that things have gotten better in recent years, but it's fair to say that they've actually gotten worse — the more senior the role I've taken, the more overt the unacceptable behavior," she wrote on LinkedIn.
In March, the Lloyd's of London insurance market announced a record 1.05 million fine against one of its members for sexual harassment and bullying.
Until 2018, insurer Atrium allowed an annual "Boys' Night Out" of heavy drinking, during which some male employees made inappropriate and sexual comments about female colleagues.
The fine was imposed as part of efforts to combat excessive drinking, sexism, and harassment in the market.