Ennis was born in West Calder, Scotland and raised in the United States. By 1900 Ennis was in charge of one of the American Bridge Company's largest sites. Ennis joined Dorman Long in 1903, and became General Manager in 1915 and a Director of the company in 1924.
- Brearley, Joan McDonald; Ennis, Lawrence (1982), The bridge opened : official opening, 19th March, 1932, Pylon Press, ISBN 978-0-9593592-0-6
- As joint author - in Minutes of Proceedings of The Institution of Civil Engineers, Vol. 238 - Session 1933-1934, Pt. 2. London: 1935. 2) Sydney Harbour Bridge: Manufacture of the Structural Steelwork and Erection of the Bridge, by R. Freeman and L. Ennis;
- Obituaries - from the Tablet Archive
- 07 May 1938 - BRIDGE BUILDER DEAD. Mr. Lawrence Ennis. A BOYHO
- Sydney Harbour Bridge
- "CLOSING OF MAIN ARCH SPAN.". The Sydney Morning Herald (NSW : 1842 - 1954) (NSW: National Library of Australia). 11 September 1930. p. 12. Retrieved 5 May 2012.
- "Mr. Lawrence Ennis' Sudden Death.". Advocate (Burnie, Tas. : 1890 - 1954) (Burnie, Tas.: National Library of Australia). 7 May 1938. p. 2. Retrieved 5 May 2012.
- "The Late Mr. Lawrence Ennis.". Advocate (Burnie, Tas. : 1890 - 1954) (Burnie, Tas.: National Library of Australia). 14 May 1938. p. 2. Retrieved 5 May 2012.
- Freeman, Ralph; Bradfield, J. J. C. (John Job Crew), 1867-1943; Pain, John Freeman; Roberts, Gilbert; Ennis, Lawrence (1935), [Sydney Harbour Bridge] : by Ralph Freeman [and others], Institution of Civil Engineers, retrieved 5 May 2012