The country's most successful club clinched their 36th title and first since 2008, finishing five points clear at the top.
It completes a remarkable turnaround for River, who were relegated for the first time in their history in 2011.
Fernando Cavenaghi scored a brace in their win over Quilmes, while Gabriel Mercado, Cristian Ledesma and Teofilo Gutierrez were also on the scoresheet.
Cavenaghi poked in the opener from close range after Quilmes goalkeeper Walter Benitez could only parry a shot.
Mercado nodded in a Jonathan Maidana corner in the 25th minute and the points were sealed just after the hour-mark.
It was in style, too, as Ledesma picked up a pass from Cavenaghi before a tremendous 30-yard effort gave Benitez no chance.
Cavenaghi was rewarded for his hard work in the 71st minute as Gutierrez played him through and he finished neatly from an angle.
Gutierrez was slipped in behind in the dying stages by Manuel Lanzini and he also finished to complete the rout.
Boca Juniors finished second on a five-match winning run as Luciano Acosta's goal saw them to a 1-0 victory at Gimnasia La Plata.
Colon and Atletico Rafaela will feature in a relegation play-off match and they claimed 2-1 wins over Olimpo and Arsenal respectively.
Relegated All Boys drew 0-0 at home to Belgrano and Argentinos Juniors, who are also going down, lost 3-2 at Rosario Central.
Godoy Cruz were 2-1 winners at home to Racing Club, Tigre edged Estudiantes 2-1 and Newell's Old Boys drew 1-1 at Lanus.
