Theodore Frelinghuysen (March 28, 1787 – April 12, 1862) was an American politician who represented New Jersey in the United States Senate.

His great-grandfather Theodorus Jacobus Frelinghuysen was a minister and theologian of the Dutch Reformed Church, influential in the founding of Queen's College, now Rutgers University, and one of four key leaders of the First Great Awakening in Colonial America.

He graduated from the College of New Jersey (now Princeton University) in 1804 and studied law under his brother John Frelinghuysen, and later, Richard Stockton.

[4] His six-hour speech against the Removal Act was delivered over the course of three days, and warned of the supposed dire consequences of the policy: Let us beware how, by oppressive encroachments upon the sacred privileges of our Indian neighbors, we minister to the agonies of future remorse.

Jackson supporters chided Frelinghuysen for mixing his evangelical Christianity with politics, and the Removal Act was passed.1 He was Mayor of Newark, New Jersey, from 1837 until 1838.

The Whig presidential candidate, Henry Clay, was not present at the convention and expressed surprise upon hearing the news.

Frelinghuysen's rectitude might have been intended to correct for Clay's reputation for moral laxity, but his opposition to Indian removal may have put off those southern voters who had suffered from their raids (William Lloyd Garrison praised his speech opposing removal in the poem "To the Honorable Theodore Freylinghusen, on reading his eloquent speech in defence of Indian Rights"[5]).