Being an experienced surveyor, he helped with establishing roads. Eventually going on to help establish a school and a post office. John Quincy Adams would name him the first Postmaster of Randolph, Pennsylvania in 1828. In 1829 white settlers asked for him to help them drive off Native Americans who hunted in the area. Brown replied, "I will have nothing to do with so mean an act. I would sooner take my gun and help drive you out of the country."
In 1831 his youngest son died at the age of 4. The following year his wife Dianthe and new born son would die during childbirth. In 1833 he would go on to marry his house keepers younger sister Mary Ann Day.  The Brown's and their remaining children would continue to live in Pennsylvania until 1836 when they moved back to Ohio. Back in Franklin Mills, (Kent) Ohio Brown  borrowed heavily buying land and operated a tannery along the Cuyahoga river with partner Zenas Kent. When the financial panic of 1837 struck Brown was facing property loss and great hardship. During the Browns stay in modern day Kent Ohio they were removed from the Congregational church for sharing their church pew with a black man.  After the killing of  Elijah P. Lovejoy  in 1837 Brown publicly vowed: "Here, before God, in the presence of these witnesses, from this time, I consecrate my life to the destruction of slavery!"

The late 1830's early 1840's he tried his hand at a number of different occupations in attempt to pay off his debts. Everything  from more surveying , farming, tanning and raising horses briefly. In 1842 he declared bankruptcy in federal court. The following year 4 of his children died of dysentery.  In the mid 1840's Brown began work in the wool industry and began building his reputation as a premier wool grading expert.

In 1846 Perkins and Brown wool company moved to Springfield Massachusetts. Brown becomes a parishioner of the prominent abolitionist "Sanford Street Free Church" (Modern day St. Johns Congressional) from 1846-1850. There he witnessed speeches from Sojourner Truth and Frederick Douglass. In 1847 Douglass stayed at Brown's home after speaking at the church. Douglass is quoted as saying: "From this night spent with John Brown in Springfield, Mass. while I continued to write and speak against slavery, I became all the same less hopeful for its peaceful abolition. My utterances became more and more tinged by the color of this man's strong impressions."

In 1849 Perkins and Brown Wool Co closed its doors after a business trip to Europe. Brown had hoped to fetch a higher price for his Massachusetts wool but it did not go as planned and the company faced heavy losses. Perkins and Brown would continue to do business with one another for a few years after this closure with Perkins taking on most of the financial hardship. Brown would nearly be out of debt by the mid 1850's.

Before leaving the Springfield area Brown helped establish a group called "The League of Gileadites" which helped African Americans resist the fugitive slave act and armed them to fight slave catchers. 

"Should one of your number be arrested, you must collect together as quickly as possible, so as to outnumber your adversaries…Do not delay one moment after you are ready: you will lose all your resolution if you do. Let the first blow be the signal for all to engage; and when engaged, do not do your work by halves, but make clean work of your enemies…”

By 1848, financially exhausted, Brown had heard of Gerrit Smith's Adirondack land grants to Black men, called Timbuctoo. Later deciding to move his family there and help establish a farm where he could provide guidance and assistance to the Blacks who were attempting to establish farms in the area. He ended up buying land in North Elba, NY (Lake Placid) where his farmstead is a state monument to this day.

By 1855 Brown had began to hear from his sons in the Kansas territory about the pro-slavery terrorism occurring to insure Kansas enters the union as a slave state.  He then begins to head to Kansas stopping along the way to obtain weapons and supplies. Arriving shortly after the sacking of Lawrence in May of 1856 Brown was furious at how non-violent the abolitionists have been to such  a violent force as the pro-slavery legislature and settlers. 

Within the week John Brown, some of his sons and a few other men would head to the Pottawatomie creek and kill 5 pro-slavery militants and officials who had threatened to burn his family out and all other abolitionists in the area. Not taking these threats lightly John Brown made a decisive blow against the pro-slavery forces who had been engaged in terrorizing abolitionists. John Brown Jr. was later captured for allegedly being part of the Pottawatomie killings.

On the 2nd of June, during what is now called the Battle of Black Jack, John Brown, nine of his followers, and 20 local men successfully defended a Free State settlement at Palmyra, Kansas, against an attack by pro slavery forces led by Captain Pate. The Captain and 22 of his men were taken prisoner. After being captured, the pro-slavery militants were taken to Brown's camp. Brown forced Pate to sign a treaty which exchanged the freedom of Pate and his men for the promised release of Brown's two sons. 

August the same year, a company of over 300 Missourians under the command of General John W. Reid crossed into Kansas and headed towards Osawatomie, intending to destroy the Free State settlements there. On the morning of August 30th they shot and killed Brown's son Frederick and his neighbor David Garrison on the outskirts of Osawatomie. Brown was outnumbered more than seven to one and arranged his 38 men behind natural defenses along the road. Firing from cover, they managed to kill at least 20 of Reid's men and wounded 40 more. Reid regrouped, ordering his men to dismount and charge into the woods. Brown's small group scattered and fled across the Marais des Cygnes River. One of Brown's men was killed during the retreat and four were captured.

The Missourians plundered and burned Osawatomie while Brown and his men hid nearby. Despite his defeat, Brown's bravery and military shrewdness in the face of overwhelming odds brought him national attention and made him a hero to many as "Osawatomie Brown".

Returning to the east to raise funds for his ultimate goal of raiding the south John Brown would return to Kansas but one more time before heading south. Late 1856-1858 John Brown is travelling all over the North East and Canada recruiting men and funds for his Harper Ferry invasion. Heading to Chatham, Ontario with 12 of his followers they had a constitutional convention. Here Brown was introduced to Harriet Tubman, who helped him recruit men for his raid. The conventions 34 blacks and 12 whites adopted Brown's Provisional Constitution.

On December 20, 1858 Brown led his own raid, in which he liberated 11 slaves, and looted horses and wagons. On January 20, 1859, he embarked on a lengthy journey to take the liberated slaves to Detroit and then on a ferry to Canada. During this journey many attempts were made to stop him. resulting in the "battle of the Spurs" and other close calls. After completing the journey to canada he traveled again through Ohio, New York, Connecticut, and Massachusetts to drum up more support for the cause.

He arrived in Harpers Ferry on July 3, 1859. A few days later, under the name Isaac Smith, he rented a farmhouse in nearby Maryland. He awaited the arrival of his recruits. In late September, the 950 pikes he ordered arrived from Charles Blair. Brown had only 21 men. They ranged in age from 21 to 49, 16 white and 5 black. Twelve had been with Brown in Kansas raids.

On October 16, 1859, Brown led 18 men in an attack on the Harpers Ferry Armory. He had received 200 Beecher's Bibles - .52 caliber Sharps rifles - and 950 pikes from northern abolitionist societies in preparation for the raid. The armory was a large complex of buildings that contained 100,000 muskets and rifles. After capturing the armory They would then head south, drawing off more and more slaves from plantations, and fighting only in self-defense.