Markey campaign spokeswoman Giselle Barry said Markey "is grateful to have support from grassroots activists and thousands of individuals across Massachusetts who support his record of standing up for middle class families and fighting the special interests."
There was also some fundraising overlap between Markey and Lynch, with some PACs backing both candidates.
Markey received the support of some of the same unions which backed Lynch, including the machinists and ironworkers PACs. And both Markey and Lynch received support from PACs representing defense contractors Raytheon, Co. and Lockheed Martin and the technology and manufacturing company Honeywell International Inc.
Although they both raised hundreds of thousands of dollars in the past election cycle, neither Markey nor Lynch faced serious competition. Each had a Republican challenger last year, but both were easily re-elected. Neither faced a primary challenge.
The primary in the special election to fill the U.S. Senate seat left vacant by John Kerry's resignation to become secretary of state is April 30. The election is June 25.
Even as they look to raise the millions needed to mount a statewide campaign, Markey and Lynch have already taken steps they say will help limit the influence of outside groups on the election.
Both Democrats have signed their version of the so-called "people's pledge" adopted by former Republican U.S. Sen. Scott Brown and Democratic U.S. Sen. Elizabeth Warren during last year's Senate campaign.
That pledge successfully kept outside groups from launching television, radio and internet ads during the campaign, although groups still poured millions into mailings, phone banks and get-out-the-vote drives.
The deal agreed to by Markey and Lynch also applies to campaign mailings.
Even with the agreement, last year's Senate contest smashed state records for the most expensive Massachusetts election ever.
On the Republican side, the field is still sorting itself out following Brown's decision not to run a third time for Senate.
The only announced GOP candidates are Daniel Winslow, a state representative from Norfolk and Gabriel Gomez, a businessman and former Navy Seal who lives in Cohasset. Former U.S. Attorney Michael Sullivan and former GOP congressional candidate Sean Bielat are also eyeing the seat.