His Democratic opponent, John Ramsey, successfully portrayed him as a flashy aristocrat who was fond of toddy and store-bought clothes, and Heiskell was defeated.
William's wife, Julia, however, supported the Confederacy, and Frederick's son, Joseph, served in the Confederate Congress.
After General Ambrose Burnside occupied the city in September 1863, William "Parson" Brownlow, a staunch pro-Unionist, was appointed special agent to the Treasury Department, and in turn hired Heiskell as an assistant.
No action was taken, though Jim Heiskell was given documents by General John Schofield asserting that he was a free citizen.
When the House convened on April 3, Heiskell was elected Speaker, defeating James R. Hood of Hamilton County by a vote of 37 to 29.
Conservative Unionists, led by Heiskell, were outraged when Brownlow threw out thousands of votes in the August 1865 congressional elections, allowing Radical candidate Samuel Arnell to win in the 6th district.
The Conservatives also endorsed Johnson's veto of the Freedmen's Bureau bill in early 1866, which Radicals in Congress and Tennessee had championed.
[15] Brownlow's Whig derided Frederick Heiskell as a "superannuated, shallow-brained, malignant, personally corrupt man.
"[16] In July 1866, Brownlow called a special session of the legislature to consider the Fourteenth Amendment, which Radicals supported, but Conservatives, including Heiskell, opposed.
The Speaker pro tempore, John Norman, signed the amendment, however, and Brownlow quickly certified its ratification.
Heiskell's brother, Frederick (1786–1882), was the cofounder of the Knoxville Register, and served one term in the Tennessee Senate (1847–1849).
A nephew, Joseph Brown Heiskell (1823–1913), served in the Tennessee Senate in the late 1850s, and represented the 1st district in the Confederate Congress during the Civil War.
Two stained glass windows in the St. John's Episcopal Cathedral in downtown Knoxville are dedicated to Heiskell and his wife, Julia.