Rise to Fame
Six years on Neighbours as Billy Kennedy gave him a career in Australia. The international one came from House M.D., where he spent eight seasons as Dr. Robert Chase. The character was written as American but the writers rewrote it around Spencer after he was cast. Most of the show's attention went to Hugh Laurie, which was probably educational. He was among the few cast members to last all eight seasons alongside the title character.
In the Spotlight
He called showrunner Derek Haas in 2021 and said he was done. By his own count, eighteen straight years of network television, going from House directly into Chicago Fire without a break. Matthew Casey's exit came in the show's 200th episode, which is a tidy way to close things out. Three years later, Last Days of the Space Age (2024) marked his return, playing an Australian on Australian soil, requiring him to re-learn the accent he'd spent a decade suppressing.
Side Notes
His father and brothers are all doctors, which makes two decades of playing medical characters feel less like typecasting and more like homework. Before any of that, he was a member of the Australian Boys Choir and reportedly deferred a Monash University spot at 18 to stay on Neighbours. He plays violin in Band from TV alongside former House co-star Hugh Laurie, and the band donates its earnings to charity, which is either very wholesome or deeply on brand for a group of TV actors who don't need the money.