With Saturday's win, Riner, 32, now has a tally of three golds and two bronze medals from his Olympics appearances.
The success helped to make up for his shock loss in Friday's quarter-finals in the men's +100kg individual contest against Tamerlan Bashaev of the Russian Olympic Committee. The Frenchman had to settle for the bronze medal.
The silver medal went to Japan and the two bronze medals were awarded to Germany and Israel.
Japan has won nine gold medals, two silvers and one bronze in the judo in Tokyo - a record haul since it became an Olympic event for men in 1964 and for women in 1992.
The new teams event meant a 15th judo gold was on offer on top of the seven weight categories each for men and women.
Three women in the -57 kg, -70 kg, +70 kg weight classes and three men in the -73 kg, -90 kg and +90 kg weights each faced off one by one in the team event.
In the final of the team contest, Riner beat Japanese gold medallist Aaron Wolf by an inner thigh throw to score a waza-ari win in a gruelling 'Golden Score' sudden-death overtime, bringing his country closer to gold in the new team contest.
His team mate Sarah Leonie Cysique followed suit, defeating Japan's Tsukasa Yoshida by a waza-ari inner thigh throw to make it a 4-1 victory.
Earlier, France squeezed past Israel in the quarter-finals 4-3, with the help of Riner, who gave Israel's Or Sasson a combination of two waza-aris -- a floating throw and a straddle hold -- to make it an ippon win.
The French then powered through their semi-final against the Netherlands.
Japan had got off to a shaky start in the quarter-finals when Uta Abe and Shohei Ono, both individual gold medallists in Tokyo, lost to Germany's Theresa Stoll and Igor Wandtke.
But Japan's four other judokas beat their German opponents to win 4-2.
The Japanese team handily beat the Russian Olympic Committee 4-0 in the semi-finals.