"We are making this initial investment because Ralph Northam and Mark Herring have been forceful champions for gun violence prevention in Virginia, while their opponents subscribe to a dangerous 'guns everywhere' agenda," Brynne Craig, a senior strategist for Everytown, said in a statement.
Everytown, a New York-based advocacy group largely bankrolled by former New York City Mayor Michael Bloomberg, has been a big spender in recent Virginia contests.
In 2015, it spent more than $2 million on television ads supporting Democratic candidates for state senate as the party unsuccessfully sought to regain control of the chamber.
Virginia allows gun owners to carry concealed firearms as long as they have a permit. Everytown, its affiliated grassroots group, Moms Demand Action, and Northam are opposed to "constitutional carry", or the right to carry concealed guns without a permit. Northam also favors a ban on assault weapons, expanded background checks and wants to restore a state law that limited handgun purchases to one each month, among other measures.
The Republican candidate in the Nov. 7 election, Ed Gillespie, is opposed to any further gun control.
Everytown is supporting Northam despite the fact that the group has clashed with his ally, Gov. Terry McAuliffe (D), over a deal McAuliffe forged with Republican lawmakers to expand the rights of concealed carry permit holders in exchange for tigher restrictions on gun ownership by domestic abusers and voluntary background checks at gun shows. Northam stood with McAuliffe last year as he signed the gun compromise into law.
Everytown pilloried the deal "as a gift to the gun lobby", criticism that McAuliffe shrugged off.
Now, volunteers with Moms Demand Action in the D.C., Maryland and Virginia area plan to canvass and to make phone calls for Northam and other Democrats.
"They stand with the majority of Virginians who know that our Second Amendment rights come with responsibilities to keep guns out of dangerous hands," said Amy McPike, a Loudoun County volunteer for the group.
Americans for Responsible Solutions, a gun control group led by former U.S. Rep. Gabrielle Giffords, has endorsed the Democratic ticket in Virginia, but has yet to announce any donations. It has spent more than $700,000 on Virginia campaigns in recent years, according to data compiled by the Virginia Public Access Project.
On the other side of the gun debate, the National Rifle Association - headquartered in Virginia - has endorsed all three Republicans running for statewide office.
The organization's political arm funded an ad in support of GOP attorney general nominee John Adams that also accused Herring of taking "away the rights of gun owners to protect themselves." This is a reference to Herring's decision to stop recognizing out-of-state concealed carry permits, since reversed by McAuliffe's gun deal.
A spokeswoman for the National Rifle Association declined to comment on the ad or how much it cost.
Adam Zuckerman, Herring's campaign manager, said "the fact that the NRA is going all in to elect John Adams shows that they know he'll be the attorney general for the gun lobby, not Virginia families."
Virginia's gubernatorial contest is the nation's marquee race this year. That status, plus lax campaign finance laws, has attracted a blizzard of outside spending.
Political arms of Planned Parenthood, the Virginia League of Conservation Voters, a Democratic redistricting group backed by former President Barack Obama and California billionaire Tom Steyer's NextGen American have commited to spend more than $8 million to support Northam and other Democrats.
The same groups, along with Priorities USA - which spent more than $200 million on behalf of Hillary Clinton and Democrats running for the Senate in 2016 - announced Thursday they will spend $2 million to coordinate with Northam on a digital ad campaign. Virginia's campaign finance laws allows candidates to coordinate with outside spending groups.
That campaign, designed to reach more than 1.2 million voters before Election Day, will mark the first time that Democratic groups are pooling resources and data to reach voters online, organizers said. They described their coordinated campaign as "first of its kind" for Democratic groups in the way they are pooling resources and data to reach voters online.
On the Republican side, the Republican Governors' Association has put in $8 million behind Gillespie and the Koch-funded Americans for Prosperity has launched an ad campaign against Northam worth at least $1.4 million.