A pillar of the Compromise of 1850, which preserved the Union until 1861, this act guaranteed federal enforcement of the constitutional provision for reclaiming runaway slaves or servants.

The statute required US marshals and deputies to help slaveowners reclaim human property; it levied a fine of $1,000 if they refused. Citizens could be deputized to assist the capture of fugitives. Criminal charges could be imposed for harboring them or obstructing capture. Free states sometimes enacted personal liberty laws to block compliance. Black and white abolitionists sued in state courts to protect runaways while supporting an underground network for their escape.