"We need to mobilise and organise just as the NRA has done," said Richard Blumenthal, a Democratic senator. "It has to be done in communities, at the grassroots."
Bloomberg's millions are intended to begin building that movement by uniting disparate gun-control groups into a single organisation under the name Everytown for Gun Safety.
The group will focus on mothers and suburban women, the voters who often decide US elections, and involve campaign-style field staff.
Despite the infusion of cash, their goals will remain relatively modest. It will focus on expanding background checks and fighting gun-trafficking rather than outlawing assault weapons or magazines capable of carrying dozens of rounds.
Bloomberg, 72, is a political independent but tends to support liberal causes such as the environment, same-sex marriage and reform of immigration laws. He said he would not hesitate to attack Democrats from conservative states who failed to support tougher gun laws, even at the risk of seeing them lose to Republicans.
"Guns are the number one thing," he said. "So I've got a senator who's running for re-election. He's terrible on guns but good on immigration. I'm going after him. That's it."
The former mayor, who is the 10th richest person in the US, made no effort to placate about 37 per cent of Americans estimated to have a gun in their home. "I think having a gun at home when you have children is really dumb," he said.
Speaking of his campaign work, he said: "I am telling you if there is a God, when I get to Heaven I'm not stopping to be interviewed. I am heading straight in. I have earned my place in Heaven. It's not even close."
