Downing v. McCartney was a United States Supreme Court case that dealt with the issue of whether a contract between two parties was valid. The case involved a contract between William Downing and John McCartney, in which Downing agreed to pay McCartney $1,000 for the purchase of a tract of land. McCartney had previously sold the land to another party, and Downing argued that the contract was invalid because McCartney had no right to sell the land. The Supreme Court held that the contract was valid, and that McCartney had the right to sell the land. The Court reasoned that McCartney had the right to sell the land because he had a valid title to the land, and that Downing had the right to purchase the land because he had agreed to pay the purchase price. The Court also held that McCartney had the right to enter into the contract with Downing, and that Downing had the right to rely on the contract. The Court concluded that the contract was valid and enforceable.

In Downing v. McCartney, the Supreme Court of the United States held that a contract between two parties was not enforceable if it had been made in violation of public policy. The case involved an agreement between two individuals to purchase and sell real estate at a price higher than what was allowed by law. The majority opinion found that such contracts were against public policy and therefore could not be enforced by either party. Justice Field dissented from this decision, arguing that while it may have been illegal for the parties to enter into such an agreement, they should still be able to recover damages for any losses suffered as a result of their breach of contract. He argued that allowing them to do so would encourage people to abide by laws governing contracts rather than risk losing money due to non-compliance with those laws.