Sanborn was a social scientist and memorialist of American transcendentalism who wrote early biographies of many of the movement's key figures.

[3] He already believed himself capable of making a stir in the world by the age of two, having held up a stick in a thunderstorm and experienced being struck by lightning.

At age nine, following careful reading of the abolitionist newspapers The National Era and Horace Greeley's New-York Tribune, Franklin announced to his family that slavery was wrong and the United States Constitution should be revised or revoked.

[4][page needed] In 1850, at the suggestion of his future wife Ariana Walker, Sanborn arranged to study with the Exeter teacher and private tutor John Gibson Hoyt.

[10] On the night of April 3, 1860, five federal marshals arrived at Frank Sanborn's home in Concord, Massachusetts, handcuffed him, and attempted to wrestle him into a coach and take him to Washington to answer questions before the Senate in regard to his involvement with John Brown.

(Sanborn's aunt Miss Alice Leavitt, his mother's sister, was personal nurse to Ralph Waldo Emerson's widow Lydian.

In 1880, Frank Sanborn built a large house on the banks of the Sudbury River in Concord, placing a plaque with the name of his first wife, Ariana, in a gable end.

[15] Frank Sanborn died February 24, 1917, of a broken hip after being struck by a railroad baggage cart during a visit to his son Francis in New Jersey.

He was buried at Sleepy Hollow Cemetery in Concord, near the graves of his friends and mentors Ralph Waldo Emerson, Bronson Alcott, Ellery Channing, and Henry Thoreau.

Walt Whitman described Sanborn as "a fighter, up in arms, a devotee, a revolutionary crusader, hot in the collar, quick on the trigger, noble, optimistic.

He was revered in the end as a relic from a golden age gone by—a tall and venerable figure moving picturesquely through Boston and Concord.

He also edited two volumes of Theodore Parker's Writings (1914), introduced Newton's Lincoln and Herndon (1913), and wrote brief biographies of Ellery Channing and of Mrs. Abbott-Wood of Lowell.