Mary H. Carr was an enterprising and respected member of Portland's early Black community. Known for her courage and resilience, she was a successful businesswoman, a leader in the Workingmen's Joint Stock Association of Portland, and a committed member of the city's first Black church. Except for two years spent in California, Portland was Carr's home from 1858 until her death in 1911. In her obituary, she was identified as a "Pioneer Negress" with an "interesting career," and the Oregon Journal published her photo.

Although information about Mary Carr's early life is incomplete, we know she was born in Pennsylvania, apparently to a father from Pennsylvania and a mother from Delaware. The 1900 census gives her birthdate as March 1836, but she was probably born earlier since she reportedly died in 1911 at age eighty-eight. Supposedly widowed at an early age, no record has been found of Carr's marriage, and she was evidently childless. Her only identified family were her deceased sister, Margaret Cannon, and her niece, Katie J. (Cannon) Briscoe, who traveled from Philadelphia to Portland for Mary's funeral. 

What drew Mary Carr to Oregon Territory in 1858 is unknown. The year before, voters had approved an exclusion clause for the state constitution that prohibited new immigration of Blacks and made it illegal for them to own real estate, which took effect in 1859. By 1860, only 128 Blacks were listed in the Oregon census. But Carr was not deterred.

During the early 1860s, Mary Carr appeared in Portland city directories as a washerwoman and laundress at the corner of First and Pine, where she established her first boarding house. An 1867 advertisement in the Oregonian named her as one of twenty Portland women and men "cheerfully recommending" the newly introduced Pioneer Washing Machine, a metal and wood machine with hand-operated agitator and wringer, selling for twelve dollars. "Easily worked by one person," the Pioneer would wash "the dirtiest clothes perfectly clean in from five to ten minutes, with but slight labor." 

The 1872 directory named Carr as the only "colored" person among fourteen boarding house proprietors. She was later remembered for ruling her boarding houses "with an iron hand" and keeping them "always in order." In 1880, for example, she placed this notice in the Oregonian: "ALL PERSONS HAVING TRUNKS, VALISES, Carpet Sacks, or Chests at Mrs. Mary H. Carr's house No. 47 Second St., will please call and settle their bills and redeem such things as belong to them within 10 days…or they will be removed from the premises. MARY H. CARR." To reach her California clients, she placed similar notices in the San Francisco Elevator.

Good dining was a hallmark of Carr's boarding houses, which led to business ventures with Edward S. Simmons (1831–1887), a talented cook. A widower from Pennsylvania, Simmons frequently boarded with Carr and for a time was proprietor of Uncle Tom's Cabin Restaurant on First Street. In 1878, the two advertised a "nice mess room for gentlemen at No. 27 Second street," in what was then "the heart of the city." Their eating house "catered to some of the most select trade in Portland," and the Oregon Journal later described Carr's patrons as "men who have since gained fame and fortune." Carr and Simmons established "two dining rooms" on Fourth and Stark in 1884. Two years later, M. H. Carr & Co.—Carr, Simmons, and Thomas L. Greene—were proprietors of the Bachelor's Home Hotel in Albina, where they promised "Meals Best to be had in Town” and “Good Accommodations for Families and The Traveling Public." 

In 1862, founders of the People's Church met in Carr’s home to organize Portland's first Black church, which was incorporated in 1869 as the Portland African Methodist Episcopal Zion Church. Always ready to support the A.M.E. Zion Church and its pastors, Carr hosted ministers and special events, raised money, and served as president (1875) and treasurer (1876) of the church society. In her dealings with the public, she was remembered for "never permitting herself to be imposed upon by anyone except negro preachers."

Carr was a founding member and active leader of the Workingmen's Joint Stock Association of Portland, which filed for incorporation on December 11, 1868, with capital stock of $50,000 (about $1,018,000 in 2022 dollars). The founding members, led by George Putnam Riley, were twelve Black men, one white man, and two Black women. On behalf of its members, the WJSA purchased properties in the Seattle and Tacoma areas of Washington Territory and often met at Carr's home. She was elected board director in 1889.

Carr also purchased and sold properties in Portland. In June 1871, she bought a lot in McMillen's Addition to East Portland for $500 (about $12,000 in 2022); she sold it in 1884 for $800 (about $24,000 in 2022). In December 1884, she sold a lot in Couch's Addition for $1,745 (about $50,000 in 2022).

A believer in women's rights and woman suffrage, Carr valued her opportunity to vote as a property owner in local elections. The New Northwest reported that she was eager to vote for School Director, a mission she accomplished in March 1889. She would not live to see Oregon women secure the ballot in 1912.

During economic hard times, especially during the 1890s, Carr struggled financially, fell behind on taxes and other assessments, and lost properties. She "suffered many financial misfortunes,” the Oregonian reported at her death, “but always recuperated her losses." In 1900, she was working as a laundress and living in a rented house with one Black and two white roomers. Within ten years, she had her own home at 455 Main Street, where her lodgers included a laundress and a church minister and his family.

To the end, Mary Carr was resourceful and independent. She died in her home on Northeast Seventh Street on December 23, 1911, and was buried at Lone Fir Cemetery, where she had purchased a half-lot. If any original cemetery marker exists for Mary Carr, it is yet to be found.