Brainerd's longtime commitment to the cause of abolition was recognized in 1854, when opponents of slavery in the Vermont General Assembly chose him to fill a five-month vacancy in the United States Senate.

A native of East Hartford, Connecticut, Brainerd was raised by an uncle from the age of nine, and grew up in Troy, New York and St. Albans, Vermont.

Brainerd was the unsuccessful Liberty Party candidate for governor of Vermont in 1846, 1847, 1848, 1852, and 1854, but his candidacies served to increase awareness of the abolitionist position on slavery.

In October 1854, Brainerd's years of advocacy in the cause of anti-slavery were recognized when anti-slavery Whigs, Liberty Party members, and Free Soil Party members in the Vermont General Assembly combined to elect Brainerd to fill a short term vacancy in the United States Senate.

[2] During the war, the area around St. Albans and Swanton was contested, with smugglers vying to move goods to the Canadian side of the border and militia patrols attempting to interdict their activities.

[3] Brainerd continued his militia membership after the war and received a commission as a first lieutenant in 1st Artillery Company, 1st Regiment, 3rd Brigade.

[7] His early efforts to expand his holdings included the purchase of 1,200 acres of swampland near Lake Champlain, which he drained, improved, and developed into a successful sheep farm.

[8] Because he was opposed to slavery, Brainerd used his home and other properties as hiding places for runaway slaves attempting to escape to Canada on the Underground Railroad.

[7] In 1839, a large, aggressive gray wolf attacked flocks and herds throughout Franklin County and became a cause for concern among farmers and townspeople.

[9] A monument commemorating his deed was later placed on Aldis Hill in St. Albans, near the spot where Brainerd caught up to and killed the wolf.

[7] Brainerd's anti-slavery views caused him to leave the Whigs in 1840 out of dissatisfaction with the party's attempts to find a compromise position on the slavery issue.

[7] In September 1854, Brainerd narrowly lost the election for a seat in the Vermont Senate in which he ran as the nominee of the Free Soil Party.

[14] The Vermont General Assembly failed to choose a successor after Upham's death, so in December 1853 the governor appointed former Senator Samuel S. Phelps to fill the vacancy.

[17] When the new legislative session began in October 1854, anti-slavery members of the legislature honored Brainerd's years of commitment to their cause by choosing him to succeed Phelps.

[7] Brainerd was subsequently chosen to serve as one of the convention's vice chairmen, and was appointed as a member of the Republican National Committee.