[1][3] In 1850, Gregory ran as a Whig in an election to choose a local delegate to the state's upcoming constitutional convention but was defeated by a pro-slavery Democratic candidate.
[3] In 1863, following Confederate General John Hunt Morgan's raid into Indiana, Governor Oliver P. Morton issued a call for volunteers to enlist to help protect the state.
Gregory and the other three Republican justices (Jehu Elliott, James S. Frazer, and Charles Ray) elected to the Supreme Court that year became known as "the Lincoln four."
Gregory wrote the unanimous opinion of the court in the famous case, Smith v. Moody, which struck down Article 13 of the Indiana Constitution that banned African Americans or multiracial individuals from settling in the state or entering into contracts.
In his opinion, Gregory claimed that African Americans should be granted citizenship and were entitled to the constitutional rights of life, liberty, and the pursuit of happiness.
However, Gregory also wrote in his opinions that African Americans were not entitled to the right to vote or the ability to hold public office, as these were not "essential characteristics of citizenship.