Brookline has gone though three major phases in regard to freedom for African-Americans.
Freedom from Brookline, the first period, occurred in the 17th and 18th centuries, when enslaved people had to leave Brookline in order to become free.
The second period, freedom through Brookline, refers to the decades in the 19th c. when a few Brookline residents served as Underground Railroad conductors, assisting African-Americans in escaping north.
The 3rd period was the work of the 20th and 21st centuries, as racism declined and African-Americans could find freedom in Brookline.

During the 18th c., we know of 2 men, known only by their first names, Peter and Prince, who escaped from Brookline.
Their owners had been Henry Sewall, Esq. and Joshua Boylston. Esq. Joshua Boylston was a member of a prominent political family. Henry Sewall was one of the largest slave owners in Massachusetts, owning 8 people. (Lorenzo Greene, The Negro in Colonial New England.)
Interestingly, Sewall was the grandson of Judge Samuel Sewall, who in 1700 had published the first anti-slavery tract in the American colonies. (Judge Sewall had earlier served as the "hanging judge" at the Salem witch trials, for which he subsequently publicly repented.)

Below are two of the 'ads' slave owners placed to recover their 'property':


From Henry Sewall, Esq.: of Brookline, on the 20th of October instant, a Mulatto servant named PETER, a slim fellow, about 16 years of age, has straight black hair and has light colored clothes. Whoever takes up said servant, and will bring him to his Master, shall have THREE DOLLARS reward, and necessary charges paid.

Masters of vessels and other persons are hereby cautioned against harbouring, concealing or carrying off said servant, as they would avoid the penalty of the law.

Boston News-letter, Nov 5, 1767.


The boy in the above image holds a copy of the original runaway ad. It reads:

Ran-away from the subscriber on 18th of November last, a Negro man named PRINCE, about 27 years of age, 5 feet 2 inches high, had men's clothes on when he Ran-away.

All Masters of Vessels and others, are cautioned against harbouring or concealing said Negro, as they would avoid the Penalty of the Law. N.B. It is supposed said Negro is gone to Salem, in order to go Privateering.

Brooklyne, Nov. 30 , JOSHUA BOYLSTON , Continental Journal, 1779

We know only two things about this man: that together with his owner, Prince marched to fight at the Battle of Lexington on April 19,1775 and that four years later Prince escaped to freedom and was not heard from again. Who knows? Perhaps he had heard his owner and his friends discuss winning independence from England?