After serving an apprenticeship with the Hunter and English company, he joined the engineering department of Trinity House, the United Kingdom's lighthouse authority.

[3] After a brief period working for the Newcastle carriage builders R J & R Laycock, he returned in 1854 to assist in the lighthouse's final completion and to marry his fiancée Mary Tregarthen.

Douglass based his plans on the proven design of John Smeaton for the third Eddystone lighthouse, which had used dovetailed granite blocks for strength.

[4] Douglass sourced his granite from the De Lank Quarries near Bodmin, Cornwall, and had it shipped to Solva on the Welsh coast where it was dressed (cut and shaped).

[5] Douglass immediately went on to supervise the construction of the Wolf Rock Lighthouse, designed by James Walker, and was appointed as Engineer-in-Chief of Trinity House in 1862.

Douglass was engaged to build a replacement for Smeaton's tower in 1877, and the new lighthouse was completed in 1882, the project being finished both without loss of life or serious injury and £18,745 under budget.