The 2009-2010 season was Gachinski's third on the ISU Junior Grand Prix circuit. He won gold in Belarus and silver in Germany, qualifying him for the 2009–2010 ISU Junior Grand Prix Final, in which he was placed 6th. Gachinski won senior gold at the 2009 Coupe de Nice. At the 2010 Russian Championships, he was placed 13th in the senior level and the gold medalist in the junior level. In 6th after the short program at the 2010 World Junior Championships, Gachinski earned enough points in the free skate to take the bronze, despite popping his planned quad.