He snapped one with a T employee credited with helping stop that runaway Red Line train.
He has posed with surprised visitors on tours of the State House.
He has mugged with school kids, police captains, and even Bruins goaltender Tuukka Rask.
Selfies have become such a trademark for the governor — a 6-foot-6 former basketball player who has "selfie sticks for arms," according to his daughter — that aides now formally schedule more time around public events, so Baker can grab a smartphone, smile, and take the photos.
The shtick is also good politics. Longtime observers say, done right, selfies communicate to voters likability, approachability, and fun. And, they say, Baker's selfie-mania works because it seems real — even if the spontaneity is now carved into his schedule.
"The reason I think it works for him is because he doesn't appear to do it with a political motivation. He appears to genuinely enjoy it — it flows from his personality," said Peter Ubertaccio, a political science professor at Stonehill College.
Politicians around the world, from Pittsfield to Perth, have embraced the trend, shooting pictures of themselves and their supporters. But Baker is notable for the frequency and passion with which he — rather than his photo companion — grabs a smartphone and snaps away.
In an interview with the Globe this week in a State House room that dates to 1798, Baker meditated on both the mechanics and the zen of his selfie taking.
He said he sees two big benefits. First, it's fun and people get a kick out of it.
Second, it's efficient for someone who is asked regularly to have his picture taken.
He then grabbed a Globe reporter's iPhone and pantomimed the drawn-out process of getting a third party to take a photo, acting out all the dramatis personae in the micro-play:
" 'Hey can I have picture?'
" 'Yeah, sure.'
" 'Oh, can we get somebody who can take the picture?'
"And then they take it and they go, 'Oh, that's not a good one — can we do it again?!' "
The governor also said selfies do away with a problem often encountered when a third party tries to snap a picture with him in it: photos that cut off the former Harvard basketball power forward's head.
And there's more.
"I like the informality of it, and I like the fact that it has a certain festive notion to it. And truthfully, it's a little more intimate than the portrait stuff, and people can do silly things if they want to. And believe it or not," Baker said, "underneath it all, I'm somebody who really appreciates silly stuff."
Asked if his selfie habit is a political plus, Baker pondered for a moment.
He said he likes to think he is an approachable person and wants to be a public official who people believe is approachable.
"I do think [selfies give] people the ability to think that that's for real," he said.
There's history, too.
Michael Goldman, a longtime Democratic political consultant and an adviser to Attorney General Maura Healey and Mayor Martin J. Walsh of Boston, noted that during Baker's unsuccessful bid for governor in 2010, the rap on the candidate was he was angry and disconnected.
In 2014, there was a total turnaround in that persona, and the perception that went with it. "And an important part of that shift," Goldman said, "was the use of selfies on the campaign trail. Nothing gives people a sense of you connecting with them like your desire to take selfies with them."
Doug Rubin, who was the top adviser to Democratic gubernatorial nominee Martha Coakley in 2014, said he noticed Baker's selfie predilection early on in the campaign.
"My first thought was: It's incredibly smart. In a social-media driven world, a selfie with the governor is going to get shared on a lot of people's [Facebook, Twitter, Instagram] accounts and it's just a great way to show people that he's out there and working hard."
Specialists say the routine also helps separate Baker, a Republican in a Democratic state, from a national GOP brand that is seen, in Massachusetts at least, as far from fun and approachable.
More often than not, selfie-taking Baker is in his goofy mode, cracking jokes and laughing easily.
But it's not only chipper Charlie that insists on capturing the moment by melding his wide wingspan and a camera phone.
Last December, about a month before he was sworn in as the state's 72d governor, Baker made a whirlwind visit to the University of Massachusetts Amherst.
There, he met one of the beneficiaries of a UMass scholarship he established in memory of his grandfather.
Baker listened as Patrice Charlot of Brockton, then a senior, told him about her studies, her double major in public health and sociology, and her aspirations for post-graduation life.
And he told her about the genesis of the scholarship fund.
"I set it up to honor my grandfather, who never went to college, but really wanted his own kids to go and was a very special guy," Baker said, emotion contorting his face, voice catching in his throat. "And I really hope you live out your dreams and change the world."
They said goodbye, and Baker headed on to his next engagement.
But the then-governor-elect turned back.
"You know what," he told Charlot. "I got to take a picture of you with me so I can show it to my father."
He put his right arm around her shoulders, clutched an iPhone with his left hand, maneuvered his thumb to the shutter button, and they both smiled widely.