Prior to first Obama campaign

In 1995, Messina was hired by Democratic U.S. Senator Max Baucus of Montana. They describe their relationship as father-son-like.^{[citation needed]} In 2002, he ran Baucus's 2002 re-election campaign. Messina "refused to let Baucus attend any debate that didn't include a third-party candidate whose skin had turned blue from drinking an anti-infection solution",^[18] which was a distraction to help take attention away from the more credible Republican candidate. Messina was purportedly responsible for creating an ad for Baucus that observers considered homophobic.^[19]

In 2005, he re-united with Baucus and became his chief of staff. Messina was integral in devising the Democratic strategy that prevented the allowance of private accounts within Social Security.^[20] Messina was credited by The New York Times Magazine as the brains behind the defeat of President Bush's plan.^[21]

Messina has also been involved with other political campaigns from Alaska to New York, including serving as an advisor to Montana State Senator Jon Tester's successful election in 2006.^[20] In 1999, he became Chief of Staff to Democratic U.S. Congresswoman Carolyn McCarthy of New York. He then became Chief of Staff to U.S. Senator Byron Dorgan of North Dakota, from 2002 to 2004. In 2004, he made $80,510 and in 2005 made $128,936.^[22][23]

Barack Obama presidential campaign, 2008

Messina was hired as National Chief of Staff for the Obama campaign in the 2008 general election.^[24] He was credited with leading the efforts to staff up for the general election and controlled a $750 million budget.^[25]

After Obama won, Messina was named Director of Personnel for the Obama-Biden Transition team, helping Obama pick his cabinet.^[26]

Barack Obama presidential campaign, 2012

Messina was Obama's campaign manager during the 2012 presidential election. In January 2011, Messina left his job at the White House and began "a rolling series of personal seminars with the CEOs and senior executives of companies that included Apple, Facebook, Zynga, Google, Microsoft, Salesforce, and DreamWorks".^[27] His goal, he said, was to learn everything he could about "organizational growth, emerging technologies, marketing",^[27] to better serve the President in his role as campaign manager during the 2012 re-election campaign.

For his work, the American Political Consultant's association named him the International Strategist of the Year.^[28]

After second Obama campaign

In January 2013, Messina became head of Organizing for Action (OFA), using the Obama For America database and other resources to support President Obama's legislative agenda in his second term. While OFA was formed in 2009 by the President-elect, it was reformed as a political-action non-profit group in January, 2013.

He founded The Messina Group,^[when?][29] a full-service consulting firm with offices in Washington, New York, San Francisco, and London.^[30]

In August 2013, Messina signed on as a consultant to the British Conservative Party, helping them successfully fend off a challenge from the Labour Party in 2015.^[31] "Whereas British pollsters consistently missed that the Tories were moving into pole position, Messina's internal numbers showed for weeks they were on course to be the largest party."^[32]

While some were surprised by Messina's move to work with the Tories, The Daily Telegraph pointed out that "this makes more sense when you consider that Mr Cameron's policies – such as support for gay marriage and confronting climate change – would probably make him a centrist Democrat in the United States."^[32] The combination of "data-driven ground game, relentless messaging and sophisticated social media is Mr Messina's signature",^[33] and as stated in The Daily Telegraph, is what Mr. Messina brought to the Cameron campaign, ultimately aiding in a stunning victory for the Conservatives.^[34] In a statement, Messina also added his personal admiration for Prime Minister David Cameron.^[35]

In January 2016, Messina was hired by Prime Minister of Italy Matteo Renzi as campaign's advisor for the constitutional referendum in December.^[36] The campaign was unsuccessful and Renzi was forced to resign as Prime Minister in its wake.^[37] Messina received 400,000 euros for his advice.^[38]

In June 2016, Messina began working with Spanish Prime Minister Mariano Rajoy,^[14] using data and targeted social media that ultimately helped Rajoy win a bigger than expected victory in that year's elections and take charge of a minority government in October of that year.^[39]

Messina worked with Prime Minister Theresa May as a campaign strategist for the 2017 United Kingdom general election.^[40] Theresa May and the Conservatives suffered a very underwhelming performance, in which she successfully remained Prime Minister, however, did not manage to keep Conservatives in the majority.^[41] For May, the election has been called a "disastrous gamble".^[42]