After completing his education, MacLaren worked in London, and then moved to the United States for his health.
His health declined, in part due to the effort that was taken to create the entries for the competitions.
He traveled in April–May 1888 to northern Italy, and in August that year to Aberdeenshire and Kincardineshire in Scotland to study castles.
The following year he established his own practice at 10 Great Queen Street, Westminster, London.
MacLaren came with architect Mervyn Macartney who also left the British Isles for his health.