A mason and builder by profession, he became the town's Master of Works and was also active on the town's political scene
as a Bailie on the Town Council, for whom he gilded the King's arms on the Tolbooth (1626, arms removed c. 1814, now on display
in St. Nicholas' Garden, Castle Street).
In the late 1640s, he suddenly emerged as a sculptor of great skill and artistry with his portrait statues of George
and Thomas Hutcheson for Hutchesons' Hospital in the Trongate (1643-50, dem. c.1795, statues moved to facade of Hutchesons'
Hall, 158 Ingram Street, 1824).
These full-length statues identify Colquhoun as one of the finest sculptors of his day in Scotland, and the statues are now regarded
as being amongst the very best of their type, scale and period in the country. They are certainly Glasgow's oldest secular statues.
The models for the Hutcheson statues, which are actually on the wrong pedestals, were the portraits reputedly painted by Anthony
Vandyck (Thomas Hutcheson, c. 1600s) and George Scougall (George and Thomas Hutcheson, 1717).
These were also to inspire
Archibald Macfarlane Shannan
in his bronze busts of the brothers in 1912-13, whilst the heads of statues
themselves were used as the models for the plaster busts in the cornice of the present Hutchesons' Hall's Grand Hall, of 1876.
Colquhoun worked again on the hospital as late as 1683, when he repaired and gilded its clock. By then, he had also made a name for
himself an inventor, with his construction of the town's first fire engine (originally housed at Hutchesons' Hospital when it was also
a fire station), and as a topographical artist, when the Town Council ordered him to provide a drawing of the town for Joan Blaeu's
Atlas Major, published in Amsterdam, in 1653.
The statues were originally painted polychrome, with their flesh tones and costumes brightly and colourfully detailed, as was the
tradition in Colquhoun's day, but were stripped and repainted white in 1805 (another important example of painted Scottish sculpture
is the statue of John Cowane on Cowane's Hospital, Stirling, c. 1649).