When Janney was still a boy his parents moved to Goose Creek (present day Lincoln) in Loudoun County where there was a thriving Quaker community.

At 18 Janney was admitted to the bar of that court, where he quickly gained the respect of his peers as well as rose through the ranks of the local Whig Party.

In 1841, Janney purchased a 580-acre tract of land from Thomas Ludwell Lee II in Loudoun County, Virginia as a summer home.

In 1839 the national Whig party held a convention to nominate its candidate for the upcoming presidential election.

The Virginia delegation preferred Clay, but he had made too many enemies in his own party so the nomination went to Harrison.

In 1850 Janney received the second highest vote total in Loudoun County as a candidate for its three-member delegation to Virginia's Constitutional Convention.

Janney ultimately voted against the proposed constitution which allowed for universal manhood suffrage, and popular election of judges and the governor (among other officials).

As the Whig party collapsed under sectional strain in the 1850s, Janney remained a committed Unionist, but his political activities dropped sharply after 1852.

When the Commonwealth called a special convention to decide its course in the coming conflict, his Loudoun neighbors again chose Janney to represent them and advocate for remaining in the Union in 1861.