The presentence report claimed that Welch had previously been convicted of three violent felonies, and thus was subject to the enhanced sentence of at least 15 years in prison under the Armed Career Criminal Act.

[8] Welch then entered a habeas corpus challenge, claiming that the strong arm robbery conviction, one of the three prior felonies, was impermissibly vague, which the District Court denied.

Three weeks later, the Supreme Court ruled in Johnson v. United States that the residual clause, under which Welch was sentenced, was unconstitutional.

[citation needed] The Supreme Court expedited the briefing process so that the case could be heard and decided within the same term that certiorari was granted.

Welch argued that because the effect of the Johnson ruling was to change the sentence range, the law should be considered substantive (and thus retroactive).

The lone dissenter was Associate Justice Clarence Thomas, who wrote that the majority had undermined "any principled limitation on the finality of federal convictions".