He mainly practiced his profession alone, except for a few years when he was a member of the law firm Fripp Henderson & McGee.

M. J. O'Connor said of Henderson, "His long and brilliant career reflected high honor on the bar of Canada.

"[7] Duncan MacTavish said of him, "His career at the bar extended over a period of many years and was marked by a large measure of success, particularly in jury and criminal cases.

[13] Henderson was senior counsel for the defense of Louis Auger after he was accused of raping a young woman in the House of Commons.

[15] In the 1926 Ontario general election Henderson lost to Albert Honeywell in Ottawa North.

[17] After Ernest Charles Drury came to power in 1919, it was rumored that Gordon Henderson would become the Attorney General of Ontario.

The Toronto Telegram said that William Raney, who became the Attorney General, was the first pick, and Henderson was the runner-up.