De Lacy was born in Sunderland, England and took his artistic training at Lambeth, South Kensington and the National Gallery. He worked initially as an illustrator for periodicals such as the London Illustrated News, Graphic, and sporting magazines. He eventually became known as a painter of Thames river shipping scenes, marine views and battle portraits.
His first exhibit was at the Royal Academy in 1889. He also held exhibitions at the Royal Society and Suffolk Street Galleries. Originally trained as an engineer, he is also known to have served in the royal navy for a time. His compositions are compared favorably to the work of his contemporary W.L. Wyllie who painted in a similar style.
Working in both oil and watercolor, de Lacy achieved a reputation for accurate portrayals of estuary shipping and ocean commerce painted with a unique enthusiasm and skill.