Muriel Siebert, a securities trader who in 1967 became the first woman to buy a seat on the New York Stock Exchange, where she used her prominence to advance women’s opportunities in a male-dominated business world, died Aug. 24 at a hospital in New York City. She was 84.

The cause was complications from cancer, according to an announcement by Siebert Financial Corp., the firm she founded and where she remained chairwoman and chief executive.

Ms. Siebert — nearly everyone called her “Mickie” — was once described by the New York Times as “probably the best-known woman on Wall Street.” Born in Ohio, she struck out for the financial capital midway through college and took a $65-per-week job as a security analyst trainee. She would have earned $75 a week as a bookkeeper but preferred the long-term earning potential to immediate gain.

By the time she forced her way onto the Big Board, she was among the most noted traders on Wall Street. She made news by becoming not only the first woman to join the NYSE but also the first to own and run one of its member brokerages. In 1977, she became the first woman to serve as New York state’s superintendent of banking.

After five years in that position, she unsuccessfully sought the Republican nomination for a U.S. Senate seat held and ultimately retained by Daniel Patrick Moynihan, a Democrat. When she returned to her brokerage, she was indisputably the doyenne of Wall Street. It was a point of pride, she said, that she could match a male colleague “Scotch for Scotch.”

Muriel Siebert was the first woman to own a seat on the New York Stock Exchange. (1977 photo by Dave Pickoff/Associated Press)

Ms. Siebert was recognized as much for her financial savvy as for her outspoken criticism of the blatant gender inequities in the business. Before her arrival at the NYSE, no women’s restroom existed near the seventh-floor luncheon club. Years into her tenure, her patience exhausted, she informed the chairman that if he did not arrange for a ladies’ room to be installed, she would provide for a portable toilet.

The chairman complied, and the incident became one of the most remarked on episodes in her career.

“Not since I was a baby had so many people been so interested in my bathroom habits,” she recalled in her 2002 memoir, “Changing the Rules: Adventures of a Wall Street Maverick,” written with Aimee Lee Ball.

A forceful mentor to younger businesswomen, Ms. Siebert recounted her own experiences to highlight discrimination in Wall Street hiring practices. In the early years of her career, when the New York Society of Security Analysts distributed a résumé with the name Muriel Siebert, she found no takers. When she changed the name to read M.F. Siebert, potential employers came calling.

As she advanced from trainee to partner at several firms, she found compensation packages to be unfairly distributed.

“I changed jobs three times because they were paying a man more than I was making for the same job,” she told the New York Times. “On one occasion, the other men objected on my behalf. They went to the boss and said, ‘She’s looking for a job and she shouldn’t be.’ I got a raise — but I left later anyway.”

Once, when a high-powered New York club advised her that the elevator was to be used only by men, she rallied the support of her male colleagues. In protest of the rule, they walked with her down the stairs and through the kitchen to the exit. She also spoke out against clubs that denied membership to women, effectively barring them from places were business deals were hammered out.

In addition to sexism, she encountered anti-Semitism, often in the form of inappropriate jokes or slurs by dining partners who did not know she was Jewish. Sometimes, the Los Angeles Times reported, she mailed the offending colleague a clarifying message:

“Roses are red, violets are bluish, in case you didn’t know it, I’m Jewish. I enjoyed lunch, Mickie.”

Muriel Faye Siebert was born in Cleveland on Sept. 12, 1928, according to information provided by her firm. (She often was reported to have been born in 1932, according to Bloomberg News, but declined to correct the mistake.)

She attended Flora Stone Mather College, a women’s school that became part of Case Western Reserve University in Cleveland. She reportedly was the only woman in her money and banking course.

She left school to find work after her father died. The search took her to New York, where she had recalled visiting the NYSE for the first time and seeing a “sea of men in dark suits.”

She said that she was forced to lie about having completed college to obtain employment. (She “came clean” after joining the NYSE.) Her first job was with Bache and Co. As an analyst, she was assigned to follow the then-undesirable fields of aerospace and entertainment and impressed colleagues with her ability, as she described it, to turn “junk” into “gold.”

She held partnerships with several firms before a client suggested that she join the NYSE. She recalled that the exchange initially refused to admit her if a bank did not lend her the bulk of the $445,000 required for a seat, and that the bank initially would not extend the loan without guarantee of her admittance. But she charged her way in.

“There was all manner of concern for my delicate ears — with several articles postulating that a woman couldn’t handle the rough language of Wall Street — and many comments about the absence of a ladies’ room on the Stock Exchange floor,” she wrote in her memoir, according to Bloomberg News.

Throughout her career, she maintained her interest and expertise in the aerospace industry that helped provide her start in business.

“Muriel Siebert is probably the only member of the New York Stock Exchange who reads Aerospace Daily under the hair dryer in a beauty shop,” The Washington Post reported in 1969.

That year, she founded Muriel Siebert and Co., later transforming it into a discount brokerage firm after the Securities and Exchange Commission changed the regulation of commissions. In 1996, she took her brokerage public under Siebert Financial.

As New York state’s superintendent of banking, she oversaw the industry at a time of deep turmoil involving bank failures and the growth of foreign banking.

“I tell you, there’s poetic justice in things,” she told the Los Angeles Times. “I regulated the bank that wouldn’t write the letter to guarantee my NYSE seat loan.”

Ms. Siebert did not marry or have children. Survivors include a sister.

Her philanthropic efforts included initiatives to improve overall financial literacy and to support female entrepreneurs and businesswomen. Ms. Siebert told women that they “just have to keep fighting.”

“Money represents power to men,” she told the New York Times, “but to me it represents freedom.”