In 1814 he and his brother August Ludwig went to fight in the Napoleonic Wars as Hessian volunteers; however, a few weeks after enlisting, his military career was cut short by an acute attack of typhus fever, which seemed for a time to have completely destroyed his memory.

[2][3] Early in the fall of 1818, he undertook the cause of several hundred communities in Upper Hesse in opposition to a government measure directed at the last remnant of their political independence, and drew up a petition to the grand duke on their behalf.

[2] There he met Charles Comte, the son-in-law of Jean Baptiste Say and founder of the Censeur, a publication which he defended until he chose exile in Switzerland over imprisonment in France.

[3] Follen came under suspicion again after the political assassination of Charles Ferdinand, duc de Berry in 1820, and fled from France to Switzerland.

His lectures, with their Unitarian tendencies, offended some of the Calvinistic ministers in the district, so Follen requested and obtained a dismissal, with a testimonial to his ability, learning, and worth.

Lafayette was then visiting the United States and sought to interest some people of influence in the two refugees, who had moved from New York City and settled in Philadelphia.

Among those Lafayette contacted were Peter Stephen Du Ponceau, a prominent lawyer, and George Ticknor, a Harvard professor.

Follen continued to study the English language and law in Philadelphia, and in November 1825 took up an offer from Harvard University to be an instructor in German.

In 1835, Charles Follen lost his professorship at Harvard due to his outspoken abolitionist beliefs and his conflict with University President Josiah Quincy's strict disciplinary measures for undergraduates.

A close friend and associate of abolitionist William Lloyd Garrison,[7] Follen's outspoken opposition to slavery had incurred the hostility and scorn of the public press.

He had been called to the pulpit of the Second Congregational Society in Lexington, Massachusetts (now Follen Church Society-Unitarian Universalist) in 1835, but the community was unable to pay him sufficiently to support his family.

In 1838 Follen became the minister of his own congregation in New York City, now All Souls, but lost the position within the year due to conflicts over his radical anti-slavery views.

Due to Follen's abolitionist positions, his friends were unable to find any church in Boston willing to hold a memorial service on his behalf.

In 1841, Follen's widow Eliza, a well-known author in her own right, published a five-volume collection containing his sermons and lectures, his unfinished sketch of a work on psychology and a biography she wrote.