Sydney Ernest Hart was born at the Lizard in 1867, one of twelve children of Thomas HART. He is described as a landscape painter in 1891 and as an artist in 1901. At both times he was still living in the family home at Polbrean at the Lizard. He exhibited jointly with his father and his brother Percival Horace in Suffolk in 1889. Sydney was also with his father on a painting trip to Norway in 1901 and appears to have settled in Norway. His Cornish coastal watercolours can probably be dated to up to 1901 and his Norwegian works to after that date.

Sydney Hart remained single. He died of pneumonia at Odda in Norway, where he was buried. His gravestone is recorded online. He appears in the Norwegian censuses of 1910 and 1920. His death is recorded in the British Consular records for Bergen in 1921.