Herbert Arthur Sinnott (January 7, 1871 – after 1923) was a Canadian educator, lawyer and municipal politician who served as the 18th mayor of Calgary, Alberta from 1913 to 1915.
Sinnott was born in Kings County, New Brunswick on January 7, 1871 to David S., a farmer, and Frances (née Taylor) Sinnott. After attending schools in Sussex, New Brunswick, Sinnott graduated from Mount Allison University with a Bachelor of Arts and started his teaching career in Gagetown as principal of a grammar school. He later taught high school in Moncton, New Brunswick before moving west to Alberta in 1900. In 1903, he became a high school principal in Calgary, the first ever to the city. He began a career in law in 1908, articling under Thomas M. Tweedie. In 1911, he was called to the bar. Around this time, Sinnott also owned and rented out various properties in the city of Calgary as well as Lethbridge.
Sinnott was elected as Mayor of Calgary and served in this position from January 2, 1913 to January 2, 1915. During his time in office, oil was discovered within the city of Calgary, and it was said that the "[whole city] quickly became oil conscious". During his trial, Sinnott admitted his guilt and was sentenced to seven years to be served in a Prince Albert, Saskatchewan jail. The magistrate had expressed that "the more grievous" crime that of the betrayal of trust of Sinnott to his clients, and that it was unfortunate that such a citizen of high of esteem, had admitted to committing the crimes.
He married Margaret Horne, a graduate nurse and daughter of a sea captain, in 1901 and had one child with her, Margaret. His wife died in 1906. A conservative in politics, during his time in Calgary, Sinnott was a member of the Ancient Order of Foresters in Calgary as well as the Methodist church.