Haynes is a keen guitarist and his first breakthrough role was busking on the streets in the Co-op advert for Christmas in 2020 to Oasis' "Round Are Way" with younger brother, Rocco.

[6] Praised for his naturalistic style of acting and flair for accents, he has filmed an array of different TV roles in many well known productions such as Gentleman Jack, Dodger, Andy and the Band, Ted's Top Ten, All Creatures Great And Small,[1][7] and Channel 4's Somewhere Boy, BAFTA nominated for best drama.

His films include comedy heist The Duke, where he starred alongside Jim Broadbent and Dame Helen Mirren, crime film The Pure and the Damned, Iniquity and The Boys in the Boat, for MGM, a sweeping story about a 1930s American rowing team where he plays the role of Joe Rantz's grandson,[8] directed by George Clooney.

Haynes's first pivotal leading role was released in the summer of 2022, for StudioCanal's The Railway Children Return,[9] where he filmed alongside Jenny Agutter, Sheridan Smith, John Bradley and Sir Tom Courtenay.

Haynes plays Thomas, the grandson of Agutter's character, in the family adventure about a group of children evacuated to the Yorkshire countryside during the Second World War.