There is nothing quite like the zeal of the reformed doubter. The high kicks of a converted wallflower are a sight to behold, too. Father John Misty is a man twice reborn, and excellent company to boot.

Backed by a full-blooded country-rock band at the start of a sold-out UK tour, the New Orleans-based musician prances louchely around the stage like Jarvis Cocker used to in late-period Pulp, a skinny white version of a soul man. He falls to his knees, flings his guitar through the air to a tech who catches it on cue, caresses syllables with his long fingers as he sings them. He was not always like this.

Now 34, the man born Josh Tillman spent long years pulling serious singer-songwriter faces, writing maudlin albums called things like Cancer and Delirium (2007). He spent many of those years playing drums for Fleet Foxes, too.

Now, he is surrounded by strobing lights and throbbing keyboards, the keening slide guitars of David Vandervelde and some bawdy band crescendos lit up in the purple of a roadside cathouse. Tillman comes on stage with the mic stand already slung across his shoulders, playing a song – I Love You, Honeybear – so saturated with sweet emotion that it would happily serve as the climax of most standard band sets. It is all about the redemptive power of love, set against an unsympathetic world in perpetual crisis.

Father John Misty has a thing or two to say about the State of Things – witnessed the angry Bored in the USA (Springsteen pun intended), which lambasts his “useless education” and “sub-prime loans”. Live, the song keeps the sardonic canned laugh track it had on the album (and on a performance on David Letterman back in February).

But tonight, most of his songs are about love. This is not the knee-jerk sentiment familiar from so much pop music – it is an emotion wrenched from the grasp of cynicism with no little glee.

Tillman was once the sort of snarky wag who operated above sincerity, deploying “our endless progressive tendency to scorn”, as he puts it on I Went to the Store One Day, the penultimate song, sung with particular tender force. There’s a little of that acid residue left, to be honest. The band have just concluded a tour of the southern US, and Tillman confesses they’ve got “Freebird PTSD”. Cambridge, you feel, probably takes Tillman’s mordant between-song humour a little differently than, say, Tulsa, Oklahoma. Halfway through the set, The Night Josh Tillman Came to Our Apartment sounds like a lovely, twinkly, country-tinged song, until you home in on the particularly mean-spirited lyrics, detailing a threesome between Tillman and people who weren’t his honeybear.

On Holy Shit, Father John lays out his former position on love more fully. “Love’s just an institution based on human frailty,” he croons, “an economy based on resource scarcity.” But two things happened to Tillman when he left Fleet Foxes. (Fleet Foxes, by the by, remain on hiatus while Robin Pecknold gets a university degree and scores an off-Broadway play). First, Tillman’s 2012 debut album as Father John Misty, Fear Fun, reintroduced the mopey longhair as a velvet-jacketed desperado fond of hallucinogenics. Like in the Jim Carrey film Yes Man, he started saying “yes” to a lot of the things – showmanship, honesty, wiggy organ sounds – he used to disdain.

I’m Writing a Novel is one of its best cuts. Rollicking like The Ballad of John and Yoko, it finds Tillman with his trousers around his ankles, accusing “the Canadian shaman” of giving him too much of something. People liked this new version of Josh Tillman. The Village Voice’s renowned Pazz & Jop poll placed it above Dylan, Springsteen and Swift at the end of the year. And then he fell in love with a film-maker called Emma.

This year’s excellent album, I Love You, Honeybear, plots the course of this miracle, from the Rorschach blots of bodily fluids on hotel sheets to the compulsive honesty. Tillman even tells his new girlfriend about the dream where he kisses his brother. “That’s how you live free,” he declares on When You’re Smiling and Astride Me, “Truly see and be seen.” Tonight, it starts as a piano ballad and ends as a soul stomper.

Compulsive honesty can make people jerks, but it’s illuminating to see it in action. On Bored in the USA, Tillman films himself with a fan’s phone, a departure from his previous “No Photography” stage backdrop. After giving it his all, he discovers the phone is not actually filming. The crowd implore him to do it again. Tillman explains that he doesn’t want to, because then we would know that all his grand gestures aren’t spontaneous, but rehearsed.