Christopher Diffey began performing at the age of 5. He was a member of the National Boys Choir, with whom he travelled to Europe, performing at St. Paul's Cathedral for Pope John Paul II and at Westminster Abbey. As an old boy of the choir he has returned to sing in their Christmas concerts at the Concert Hall, performing traditional Irish carols.

He was in the VSO production of La Bohème in 1993 as a child. He has performed in the Lyric Opera Company production of The Saint of Bleecker Street, playing the role of a young man, as well as being lead solo in St. Mark's Easter passion, as broadcast on radio station 3 MBS FM. He sang the lead Tenor solos for Opera In The Alps, 2004 with Orchestra Victoria under Thomas Woods.

Among other pieces performed was the World Premiere of the Gordon Kerry work Through the Fire. This piece was successfully received, so much so that it was performed for Opera In The Market, 2004, where again, Christopher was one of the principal tenor soloists, along with David Hobson. He received the Pat Nicholson Memorial Encouragement Award at the 2004 Annual National Liederfest. Other performances include the 2005 Elgar Festival performances of The Kingdom and The Apostles as St. John [narrator], held at St Patrick's Cathedral in Melbourne.