Although Mary’s parents were lifelong Republicans, in 1928 she and her brother Averell declared their support for Democratic presidential candidate Al Smith. Mary’s active work for the campaign brought her once again in close contact with her friends Eleanor Roosevelt, one of the first members of the New York Junior League, and Frances Perkins, who both campaigned for their candidate throughout the country. While Republican Herbert Hoover won the election that year in a landslide, for Mary, what was to become a tireless life in politics had taken off.

Four years later, the economic prosperity of the country was gone, and the Great Depression, which would last throughout the decade, had taken its place. With her good friend Franklin D. Roosevelt heading the Democratic presidential ticket, Mary was not about to miss an opportunity to promote the vote, and in September of that year, hosted a memorable debutante party for her daughter, Mary Averell. Interested in raising consciousness on rural issues – an enormous issue at a time when up to 30 million Americans (out of a population, in 1930, of 123 million) lived and worked on farms – Mary gave a “barn dance” for over 1,000 at her Long Island estate. The invitations requested overalls instead of black tie; décor was cornstalks and vegetables; the dinner was ham, eggs, cereals and apple sauce. Since so many of the young guests would be voting in just two months, mock voting machines were brought in (with FDR’s name prominently listed on the ballot).

FDR went on to win the real election in November, and within just a few months, many of Mary’s friends and political associates were on their way to Washington to work with the new administration. When Frances Perkins accepted the appointment as Secretary of Labor, Mary decided it was time to join them.

Perkins’ appointment was not without criticism. It was objected to by many and for a host of reasons: she was not qualified; she was not a part of the labor movement; and mostly, because she was a woman in a “man’s job.” On a personal level, Perkins did not help herself with the media, with whom she was often impatient owing to their “irrelevant” personal questions or requests to comment on policy decisions that had not yet been made.

When Perkins “seriously considered” the idea of living in a convent as a way to keep some of her private life out of the public eye, Mary provided a perfect alternative. The two women shared a rented house in Georgetown, where Mary reprised her role as hostess of glittering parties for a mix of people of widely varied backgrounds. Although Mary supported Perkins’ important work, “hostess” was not the only job title she craved.  With typical enthusiasm, Mary set forth to make her own impact on the nation’s political stage.

In June of 1933, Mary was appointed by FDR to chair the Consumer Advisory Board of the National Recovery Administration (NRA). It was the goal of the board to see that the retail price of goods would not increase proportionally more than wages, to combat price mark-ups, and to protect farmers cooperatives from price discrimination. As The New York Times wrote in Mary’s obituary, she “had been recognized in and out of the administration as the chief driving force and influence of the New Deal in its approach to consumer problems.”

During this first year in Washington, she also founded Today magazine. Mary had long been interested in entering publishing, for the freedom it would allow her to promote her own progressive views and opinions on politics and society. (After her death Today acquired a competing publication, News Week, the merged publications becoming the magazine we know today as Newsweek.)

One of the most lasting of Mary’s endeavors, and indeed, one of the last, was the co-authoring of the Social Security Act along with Frances Perkins. As a result of the work of these two women and others on the committee, the retirement security of many millions of Americans had been achieved.

On November 17, 1934, Mary had traveled to her farm in Virginia for the weekend, to celebrate her 53rd birthday. During a fox hunt, Mary’s horse fell, and before she could stand up, the horse rolled over her. She fractured four ribs and suffered a compound fracture of her right thigh.

While the initial prognosis for her recovery had been good, it soon became apparent that internal damage was more serious than originally thought. Complications developed, and Mary died on December 18. After funeral services in Washington, Perkins and Eleanor Roosevelt accompanied her casket to the Harriman family estate in Arden, where Mary was buried next to her parents.

Mary’s death was noted prominently in the news. On the day of her funeral, the editorial page of The New York Times noted that her tragic accident had “ended a life of rare beauty and service.” At a memorial service a year later, Eleanor Roosevelt said quite simply, “She helped all those she came in contact with who needed her assistance.”