The group consists of pro-democracy networks, including iLaw, Ratsadon and ConForAll.
A ConForAll representative said this petition was important as everyone wanted to make sure the amendment of the Constitution would be democratic.
He said it would be the first time that the referendum was petitioned by the people, adding that the group got 212,139 signatures compared to its target of 50,000.
"This would mark an important step on constitution amendment," he said.
He expects the EC to submit the petition to the Cabinet quickly, but vowed to monitor the submission progress closely.
Yingcheep Atchanont, the executive director of iLaw, said this move proved that nothing could silence the people's voice. He made the remark after the EC earlier told the activists that it would not accept signatures collected via an online platform.
He added that this petition submission was successful thanks to cooperation from the people, and hoped that the EC would work on this issue as soon as possible.
He also vowed to put all efforts to ensure that the people of the country got a democratic constitution.