Fetherstonhaugh began his career with the patent law firm Donald C. Ridout & Co, where he was a draftsman along with Charles Riches and James E. Maybee before his call to the bar in 1889.
One year after his bar admission, in 1890, he formed his own firm, Fetherstonhaugh & Co., where he took up practice as a patent lawyer.

The firm Fetherstonhaugh & Co. opened its first location on the second floor of the Bank of Commerce Building at 19-25 King St W, and was the first tenant of the building.
His patent law practice expanded quickly.
In 1895, an Ottawa office was opened at 7 Elgin St, managed by T.S. Young.
In 1896, he opened a Montreal office with his brother Edward James Fetherstonhaugh.
By 1905, offices had been opened in New York City (managed by Albert T. Nathan, a former patent examiner) and in Washington, DC.

In 1904, Russel S. Smart joined his firm as the manager of the Ottawa office.
Smart later took over the legal practice of the firm while Fetherstonhaugh continued his patent agency, forming a partnership that has continued to this day as Smart & Biggar/Fetherstonhaugh.
By the time of Fetherstonhaugh's death in 1945, several more offices had been established across Canada, including in Hamilton, Vancouver, Winnipeg, Halifax, and Saint John.

During his career, Fetherstonhaugh was recognized as a leading expert in his field and was regularly consulted by Parliament regarding legislative amendments to patent laws and regulations.
Around 1905, he advocated for uniformity of patent legislation within the British Empire, arguing that it would enhance scientific progress and reduce costs for inventors obtaining patents in multiple jurisdictions.
In support of this proposal, Fetherstonhaugh drafted the Empire Patent Act, which was designed to coordinate the policies of patent offices across the British Empire.
However, his proposed unification of patent laws in the British Empire never came to pass.
Fetherstonhaugh was made a King's Counsel in 1910.
Fetherstonhaugh began his career with the patent law firm Donald C. Ridout & Co, where he was a draftsman along with Charles Riches and James E. Maybee before his call to the bar in 1889. One year after his bar admission, in 1890, he formed his own firm, Fetherstonhaugh & Co., where he took up practice as a patent lawyer.
The firm Fetherstonhaugh & Co. opened its first location on the second floor of the Bank of Commerce Building at 19-25 King St W, and was the first tenant of the building. His patent law practice expanded quickly. In 1895, an Ottawa office was opened at 7 Elgin St, managed by T.S. Young. In 1896, he opened a Montreal office with his brother Edward James Fetherstonhaugh. By 1905, offices had been opened in New York City (managed by Albert T. Nathan, a former patent examiner) and in Washington, DC.
In 1904, Russel S. Smart joined his firm as the manager of the Ottawa office. Smart later took over the legal practice of the firm while Fetherstonhaugh continued his patent agency, forming a partnership that has continued to this day as Smart & Biggar/Fetherstonhaugh. By the time of Fetherstonhaugh's death in 1945, several more offices had been established across Canada, including in Hamilton, Vancouver, Winnipeg, Halifax, and Saint John.
During his career, Fetherstonhaugh was recognized as a leading expert in his field and was regularly consulted by Parliament regarding legislative amendments to patent laws and regulations. Around 1905, he advocated for uniformity of patent legislation within the British Empire, arguing that it would enhance scientific progress and reduce costs for inventors obtaining patents in multiple jurisdictions. In support of this proposal, Fetherstonhaugh drafted the Empire Patent Act, which was designed to coordinate the policies of patent offices across the British Empire. However, his proposed unification of patent laws in the British Empire never came to pass. Fetherstonhaugh was made a King's Counsel in 1910.
F. B. Fetherstonhaugh