Simon Pegg is on a roll. Suddenly, interviews have a whole new appeal for him. For the first time, he says, "I've actually had something to talk about, rather than telling a story about a funny thing that happened on set".

Pegg has been discussing the philosophical ideas of his latest film, Hector and the Search for Happiness, as well as launching the occasional defence against those he feels have missed the point of it all.

The film is the story of a psychiatrist (played by Pegg) who suddenly quits his practice and his long-term partner to go on a round-the-world quest for meaning. The comedy might light-heartedly show Hector jotting down dictums about what he has learned, but it also contains what Pegg regards as serious reflections about the nature of happiness, which he says has really come into focus for him.

He didn't have any blinding revelations as a result of making the movie, he is quick to add, "but it certainly helped me to understand things".

"One of the most important, for me, was the whole thing of happiness as a process, not as an end. You can't be happy every day, it's impossible, because otherwise you'd be in a state of a kind of consistent numbness; you would have nothing to compare it to."

But happiness, he says, warming to the theme, "also helps you to understand being unhappy, in a way. If you understand what happiness is, it helps you understand every single emotion you have, as part of a larger process".

For Pegg, the film starts to take off when Hector dons his traveller's clothes. "It's the moment of unlocking his inner Tintin." (Pegg, as it happens, has a cinematic connection to Tintin. He and his friend and regular collaborator Nick Frost were the voices of the bumbling detectives Thomson and Thompson in The Adventures Of Tintin, Steven Spielberg's motion-capture epic.)

"He goes from being this buttoned-up adult to this kind of guileless adventurer," he continues.

"The movie is about tonal shifts ... when you go from joy to sadness in a breath. That's what the emotional spectrum is all about, and you have to know every single colour in order to truly know what happiness is.

"For me, the most important of the dictums that Hector writes down is the one that says 'avoiding unhappiness is not the way to happiness'. That strikes the loudest chord for me."

Hector, based on a bestselling novel by French author Francois Lelord, is directed and co-written by Peter Chelsom. The cast also includes Christopher Plummer, Toni Collette, Stellan Skarsgard and Jean Reno. Rosamund Pike, in cinemas now in David Fincher's dark thriller Gone Girl, plays Hector's girlfriend, Clara, with whom he had settled for a relationship of comfort, stasis and a degree of monotony.

Pegg and Pike have worked together before, in The World's End, the third instalment of the famed "Cornetto Trilogy" created by Pegg, Frost and director Edgar Wright, which made its debut with the heartfelt zombie comedy Shaun Of The Dead. After Pegg and Pike became friends on set, Pegg created the Twitter hashtag RosWatch. With her permission, he posts pictures he's taken of her each time they meet. It began with a shot of her asleep on the floor during reshoots of The World's End.

Pegg says he made the most of the travel in Hector And The Search For Happiness – Europe, Asia, Africa, the US – but found it difficult to be separated from his wife and young daughter for weeks at a time. "But to get to see places I wouldn't ordinarily see – and also parts of those places you would never see as a tourist, particularly in South Africa – was absolutely fantastic.

"I'd watched that country from afar as a young activist, a 16-year-old wearing my anti-apartheid badge and refusing to eat grapes for 24 hours or whatever, but to actually go there and see it up close ... was amazing, and educational and very, very moving."

Some film reviewers have taken issue with the way Hector's overseas destinations have been characterised. For Pegg, in the world of the movie, "China becomes a place that is mysterious and tempting, and Africa is the dark continent of old ... It's how those places would be described in a children's book. I read a couple of reviews that totally didn't get that, that said, 'that's just racist'. For me that was quite a bone-headed reduction [of] what the film is about."

The point, Pegg insists, is that the uptight Hector is "a terminal adult who has lost his childhood self", and so the story is told from a child's point of view. "The idea is that there is value in retaining your innocence a little bit because it helps you access your emotions as an adult."

Pegg made his first foray into Hollywood moviemaking in 2006, playing tech whiz Benji Dunn in Mission: Impossible III. He was Scotty in J.J. Abrams' new take on Star Trek; the voice of Reepicheep the mouse in The Chronicles of Narnia: The Voyage of the Dawn Treader, and of Buck the one-eyed weasel in Ice Age: Dawn Of The Dinosaurs. His recent movie-making travels have included a journey to Western Australia to appear in Kill Me Three Times for Red Dog's director, Kriv Stenders. "It was a really fun experience: a crime caper that doesn't take itself too seriously," Pegg says.

His next couple of projects are closer to home. When we spoke, he was just about to start Mission: Impossible 5, and after that, Star Trek 3.

Pegg suggested around the release of The World's End last year that he and Frost might "take a break" from their working relationship and "maybe we'll do a bunch of stuff apart, to change the way we're regarded". But he confirms now that the Cornetto trio have more in store.

"I am going to be blockbusting for the next seven or eight months, and then more stuff with Edgar and Nick," he says. "There are things that I am developing as a producer and writer, and possibly director. I'm busy for the next year and a half, and after that we'll just wait and see." 

The search for happiness: five films to get you started

Happy-Go-Lucky
Never has the downside of good cheer been more evident than in Mike Leigh's tale of a primary school teacher (Sally Hawkins) whose sheer, almost impossible, optimism makes those around her cranky and irritable.

Chronicle Of A Summer
"Are you happy?" is the question posed to ordinary Parisians in this 1960 documentary by Edgar Morin and Jean Rouch, and from this question flow so many others –  about politics, work, money, repression, inner life, the past and the present.

Eat Pray Love
Julia Roberts stars in Ryan Murphy's fictional version of a bestselling memoir by Elizabeth Gilbert about a woman's search for equanimity in Italy, India and Bali.

Happiness
French documentary maker Thomas Balmes explores what happens in the tiny kingdom of Bhutan – where a "gross national happiness" index is calculated – when a decision is made to bring TV to the country.

Groundhog Day
Harold Ramis's movie is full of many pleasures and many subjects: one of them is happiness, and how to find it without looking for it. Bill Murray's cantankerous weatherman learns many things when his life is turned into a loop of daily repetition.