His education was completed under architect David Cousin who inherited his father's architecture firm.
[2] In May 1867, Henderson emigrated to Australia to join Alexander Davidson's firm in Rokewood, Victoria.
Several large commissions in late 1868 helped catapult the venture into financial success which enabled Davidson to send money home to his family in Scotland.
The next few years brought several financial hardships to the firm resulting from a series of unfortunate incidents, including disputes with contractors and a depression in the wool industry which effected the economy of Geelong.
In April 1876, Henderson and Davidson once again dissolved their partnership; this time permanently and on somewhat hostile terms.
He left Australia for Scotland a few months after dissolving his relationship with Davidson and in early 1877 formed an official partnership with Hay.