Dominick David Black made his first appearance in Kenosha County Circuit Court on Monday after prosecutors charged him with two felony counts of intentionally of selling a gun to a minor, The Washington Post reported.
Authorities said Black purchased the rifle used in the shootings for Rittenhouse in April.
Rittenhouse is accused of shooting and killing Joseph Rosenbaum, 36, and Anthony Huber, 26, while critically injuring Gaige Grosskreutz, 26.
Rittenhouse's legal defense argues their client fired on the three victims out of self-defense, saying that the teen was fleeing as protesters chased after him, allegedly attempting to grab his gun.
"Kyle did nothing wrong," his lawyers said in a statement obtained by the Post in September. "He exercised his God-given, Constitutional, common law and statutory law right to self-defense."
Rittenhouse, 17, was too young to have legally purchased the Smith & Wesson M&P-15 rifle he carried through Kenosha the night of the shooting.
Protests had erupted in the Milwaukee suburb after the shooting of Jacob Blake by police. Tensions were already high after the police killing in Minneapolis of another Black man, George Floyd.
Robert Keller, who represents Black, said his client had no criminal history but did not comment about Black's charges, the Milwaukee Journal Sentinel reported. The Hill contacted Keller for an additional statement but did not immediately receive a response.
Last week, a judge set Rittenhouse's bail at $2 million. He will return for another hearing on Dec. 3.
Online court records show a judge set Black's bond at $2,500, and he is set for another court date on Nov. 19.