Samuel Johnson's first foray into television started with small roles in various shows including the role of Prince Jobah in The New Adventures of Ocean Girl; as Sally Fletcher's first boyfriend, Gus Bishop, in Home and Away; and in other bit parts including Blue Heelers, Halifax f.p., Stingers and Something in the Air.
His break, however, came in 2001 when he was chosen for the role of the scruffy, womanising writer Evan Wylde in Channel 10's drama series The Secret Life of Us. Evan was a main character, also narrating the majority of the show (apart from instances narrated by Deborah Mailman's character Kelly Lewis). This made Johnson a household name and earned him an AFI Award in 2001 for Best Actor in a Leading Role in a Television Drama Series.
The Secret Life of Us enjoyed consistent success up until the third series, when many major characters left, resulting in a drop in ratings. Johnson's character Evan (one of the last three original major characters alongside Kelly Lewis and Simon Trader) left early in the fourth series in 2004 and the show was axed soon afterwards.
In 2003, during the height of Johnson's Secret Life career, he received rave reviews for his performance in the mini-series After the Deluge. It follows the story of the Kirby family; their father Cliff is in the advanced stages of Alzheimer's disease, and relives his disturbing memories of the war and his first love, as a part of his experiences of the present. His three estranged sons Alex (David Wenham), Marty (Hugo Weaving) and Toby (Johnson) are thrown together to care for their father whilst struggling with their own lives and relationships and attempting to come to terms with their father's mental state.
Apart from Johnson's appearances on many Australian shows to promote his work, he has also featured on Thank God You're Here and The Panel as well as the ABC documentary The Sum of Sam; documenting his personal struggles and work with Open Family Australia, a youth outreach program co-founded by South Melbourne parish priest Fr Bob Maguire.
Johnson appeared in the police drama Rush in Melbourne, a drama revolving around Melbourne's Tactical Response team (based on Critical Incident Response-style teams). He played the role of communications specialist Leon Broznic; alongside Callan Mulvey and Catherine McClements who played Evan's girlfriend Carmen in The Secret Life of Us.
In 2010, he made a cameo appearance as an old friend of Sarah's in the final episode of Wilfred.
In 2016, Johnson starred as Molly Meldrum in the miniseries Molly.
In 2019, he competed and won the 16th season of Network 10's Dancing with the Stars, with professional partner Jorja Freeman, and raised $50,000 in prize money for his charity: Love Your Sister.
