[9] John Rock then decided to transfer into the field of dentistry and, after an 1849 apprenticeship with Dr. Harbert, a white dentist, opened a dental practice in Philadelphia in January 1850.

In 1853, Rock decided to change locations to Boston, which many at the time considered to be the most liberal city in the United States for African Americans.

Like other abolitionists in the movement, such as George T. Downing and Robert Purvis, Rock became a renowned public speaker and campaigned for equal rights.

He was a part of the National Equal Rights League with other famous abolitionists such as Henry Highland Garnet, Frederick Douglass, and John Mercer Langston.

Dred Scott, a slave, wanted to sue for his freedom, but on March 6, 1857, it was decided that the Missouri Compromise of 1820 was unconstitutional, and that African Americans were not intended to be citizens under the law.

Rock is credited with coining the phrase "black is beautiful" during a speech he gave in Faneuil Hall in March 1858 as a refutation of the Western idea that the physical features of African Americans were unattractive.

[5][12] Rock's polished speeches were printed in William Lloyd Garrison's The Liberator as well as in general newspapers,[13] promoting these central ideas.

[4] He returned to Boston in February 1859, and in 1860, under his doctors' stipulations to cut back on his workload, he gave up his medical and dental practices and began to study law.

In 1862, he spoke at the Anti-Slavery Society in Boston, where he voiced his opposition to Lincoln's plan for the so-called "negro colonization" in Haiti and sided with Frederick Douglass on several issues.

[4] It was thoughts similar to this one, in addition to the lack of executive action for African Americans, that led him to strive to attain the next level of achievement.

On February 1, 1865, the day after Congress approved the Thirteenth Amendment ending slavery, Charles Sumner introduced a motion that made Rock the first black attorney to be admitted to the bar of the Supreme Court of the United States.