Adams argued on behalf of Massachusetts native John Peck in the famous case of Fletcher v. Peck (1810). The case involved a Georgia state law that invalidated the sale of more than thirty million acres of land to several Northern companies. It was alleged that several Georgia legislators received bribes for their votes approving the land deals.

The law invalidating the land sales presented problems for innocent third parties who purchased the land without knowledge of the shady origins of how the land was first acquired. In what some historians think was a contrived lawsuit—many believe the plaintiff and defendant planned the lawsuit together—Robert Fletcher of New Hampshire sued John Peck of Massachusetts in 1803 to establish his valid claim to the land.

The Court ruled that the Georgia law invalidating the original land sales was unconstitutional because it violated the Constitution’s Contract Clause, preventing states from impairing the obligations of contracts. Chief Justice Marshall reasoned that the new law could negatively impact innocent, third-party purchasers like Fletcher.