Originally a Whig, and later a Republican, while serving in the Assembly in the 1840s Slingerland was active on the side of the tenants during the Anti-Rent War, when the renters of the Albany area's small farms rose up against the effort of the Patroons to collect long-overdue back rents.

Their efforts led to the end of the manor system that had empowered and enriched a few large landowning families since the founding of New York in the early 1600s.

Slingerland was also an antislavery activist; his work to publicize the 1848 Pearl incident while serving in Congress generated national headlines that caused advocates of abolition to increase their efforts to end slave trading in Washington, DC.

[4] During its existence, the company built and maintained a toll road from Albany to Gallupville, which passed through New Scotland, New Salem, and Berne.

[7] In 1848 Slingerland made national headlines when he alerted anti-slavery activists to the plight of more than 70 slaves who had attempted to escape Washington aboard a ship, The Pearl.

[8][9] The publicity Slingerland helped generate had the effect of causing abolitionists to increase their efforts to end the slave trade in Washington.

[7] In 2018, an article in the Albany Times Union detailed ongoing efforts to preserve the Slingerland family vault.