Theodore attended the Rutgers Grammar School and worked as a writer and proofreader for the Fredonian until the age of sixteen, when he entered into a mercantile career, primarily based in the American South.

[1] At twenty, he moved to Vicksburg, Mississippi but returned to Jersey City in 1850 to work in his father's extensive coal and iron business.

[2] After admission to the bar in 1848, Randolph entered politics as a member of the Whig Party who supported states' rights and consistently opposed the abolition of slavery, like his father.

In the Assembly, he sat on the Special Joint Committee on National Affairs, leading the unsuccessful effort to avert the American Civil War.

[1] In November 1861, following the outbreak of the American Civil War, Randolph won a special election to fill a vacancy in the New Jersey Senate.

[1] In the Senate, Randolph was the chief ally of Governor Joel Parker, and they joined in criticism Abraham Lincoln's operation of the war while opposing anti-war efforts.

[1] He also introduced a relief bill in 1865 to extend equal benefits and enlistment bounties to black soldiers, arguing that whites should not do injustice to an "inferior" race.

His prison reforms were partly motivated by an interest in making the system self-sustaining by improvement management and increasing the productivity of convict labor.

On recommendation from a special commission, Randolph urged the legislature to expand Trenton State Prison and create a "house of correction" to employee short-term convicts in an environment free from hardened criminals.

[1] In education, Randolph's administration expanded the free public school system statewide and laid the groundwork for a new "lunatic asylum" in Morris Plains, which opened in 1876.

The legislature passed a stringent law that disenfranchised the recipient and provider of any election bribe and put guilty corporations in jeopardy at losing their charter.

His vetoes included bills which would, in his view, promote railroad expansion at taxpayer or property owner expense and reorganize municipal government for partisan purposes.

[1] In July 1871, Randolph averted a threatened riot in Jersey City when he prevented Irish-Americans from disrupting a parade planned by Orangemen on the anniversary of the Battle of the Boyne.

After leaving office in January 1872, he actively campaigned to recruit a Democratic alternative to Ulysses S. Grant and Horace Greeley.