Now he is about to find out if the dutiful note taking and occasional turn behind the microphone have paid off as he takes over the briefing room podium and becomes the public face of the Obama administration.
“There’s an advantage to having watched basically every single White House press briefing in the last five years because so much of that job, it’s not about putting points on the board, [success] is in the eye of the beholder,” Earnest explained. He talked shop with the Washington Examiner in his longtime office in a backstage area known as “lower press,” which he'll soon leave for a desk just outside the Oval Office.
"It can't only be about avoiding the problems," he said of the need to make a public case for the president's policies.
His quiet confidence is rooted in years as the behind-the-scenes source for information in an insular White House, cultivating goodwill among reporters increasingly peeved about their lack of access to Obama.
But don’t expect a lengthy honeymoon for the man blessed with the most fortuitous name of any White House press secretary.
Earnest, 39, takes on the job as Obama's approval ratings hover around 40 percent, the White House agenda competes with the 2014 midterm elections and a growing chorus of critics questions the relevance of the daily briefing altogether.
White House officials say Obama selected Earnest mainly because he trusted the Missouri native. And with little time before the lame-duck phase of his presidency, Obama could ill afford a messenger in need of on-the-job training.
Though probably not a job requirement, the president also can relate to Earnest on another level: sports.
Earnest played basketball and baseball at a Kansas City prep school and will surely find ways to promote his beloved Royals and Chiefs to a national audience whenever possible.
Earnest, who has been serving as Jay Carney's deputy and occasional fill-in for briefings, is an Obama loyalist, part of the administration since its inception. The Rice University graduate was Obama's Iowa communications director, crafting his message in a state that catapulted Obama to the presidency.
His wife, Natalie Wyeth Earnest, is the assistant Treasury secretary for public affairs and is expecting their first child.
Before joining Team Obama, Earnest worked on a Houston mayoral campaign, on New York City Mayor Michael Bloomberg's first campaign, as an aide to Rep. Marion Berry, D-Ark., and as a spokesman for the Democratic National Committee.
“I’m sure you will at some point get frustrated with him as well,” Obama told reporters when announcing Earnest’s promotion, “but it’s going to be hard, because he’s a straight shooter and a great guy.”
Earnest will have more trouble keeping the great-guy label as he becomes the administration's first line of defense for questions ranging from the trade for Sgt. Bowe Bergdahl, deadly lapses in medical care at Veterans Affairs hospitals and unforeseen controversies that await all press secretaries.
Carney’s briefings grew more contentious later in his tenure, a reflection of Obama’s mushrooming political problems. But Earnest, some of his predecessors said, is uniquely suited to improve relations between the Obama White House and the press.
His advocates say the low-key Earnest could reduce the level of combativeness that the Obama press shop has displayed in the past.
“Tell every senior White House official they are no longer allowed to call reporters and scream,” Mike McCurry, the former press secretary for President Bill Clinton, said of advice he would offer Earnest.
“They can register complaints, but constant barrages lose effectiveness when used in overabundance,” he added.
Earnest’s main problem, however, isn’t reporters’ hurt feelings. It’s fighting perceptions that the White House is unable to exert influence on Capitol Hill or effectively implement its initiatives.
“We see in them the frustrations and hopes of a president,” Martha Joynt Kumar, a presidential historian who focuses on White House communication, said of press secretaries.
“Jay has been a lightning rod for the president's doubters who have heaped criticism on him as a stand-in for the president,” she added. “Josh is known for his hard work and willingness to provide answers to reporters’ questions. There are limits, though, in this administration to how much information White House officials want to divulge."
A White House correspondent with more than 20 years’ experience put it another way: “I like Josh a lot. But ask me again in a few months. The press secretary job has that effect.”
One advantage that Earnest has over his predecessor is deeper connections to the president. A former reporter turned communications director for Vice President Joe Biden -- in other words, an outsider -- Carney faced doubts about whether he truly had Obama's ear.
“You have to know what’s going on,” said Ron Nessen, press secretary for Republican President Gerald Ford. “That’s the single most important thing. Otherwise a staff member puts his own spin on it. That’s bad.”
Earnest will soon find out whether his years as an understudy will serve him well in a starring role.
“There have been times when we’ve occupied more political high ground than we do now,” Earnest conceded. “That’s going to ebb and flow. I welcome the challenge — I’m OK with dealing with a little pressure."