The Chained to the Rhythm hitmaker was joined by the former Canadian prime minister at the Crazy Horse Paris cabaret theatre to celebrate her 41st birthday on the weekend.
Pictures obtained by TMZ showed the couple walking out of the French venue holding hands and smiling at one another, with Katy wearing a vivid red dress and the 53-year-old politician in an all-black outfit.
The pair were first romantically linked earlier in 2025, when they were spotted on a date in Montreal, Canada, shortly after the Dark Horse singer split from fiance Orlando Bloom in June.
They were next photographed together in September, kissing on a yacht off the coast of Santa Barbara.
Earlier in October, it was reported the pair were "quite taken with each other".
"They have stayed in touch since the middle of summer but haven't been able to spend that much time together, due mainly to her schedule," a source explained to People magazine.
"Justin is also busy and both have family obligations. They have interests in common. Both are taking dating as it comes. But they are definitely into each other - and have been."
The insider noted the pair's romance has been allowed to develop slowly and "in addition to the attraction, they are both smart and love to talk about serious issues.
"Justin thinks she is terrific. It has had time to develop on a friend and intellectual level as well as supersized attraction. The romance has merit," the source said.
Another source previously said Katy and Justin "have a lot in common".
"They are interested in each other, but it will take a while to see where this goes," that person told People at the time.
"She is travelling around the world, and he is figuring out his life now that he is no longer prime minister of Canada, but there is an attraction. They have a lot in common.
"Music is one of many things they can share. Both are idealists and still live in a world where they think they can make improvements, although it has gotten more difficult."
Justin has Xavier, Ella-Grace, 16, and Hadrien, 11, with ex-wife Sophie Gregoire - who he split from in 2023 - while Katy is mother to five-year-old Daisy, her daughter with Orlando.
"Their own personal responsibilities could make this relationship move slower than it would, but there are ways to see the other and still fulfil their parenting responsibilities," the source said.
"For one thing, they each have an ex. So, duties are split in half. And long-distance relationships, while still hard, are possible for these two."
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