Naval architect. Born in Stranraer (Dumfries and Galloway), Rennie became an apprentice shipwright on the Clyde at Govan but, determined to better himself, studied naval architecture in the evening. He worked in Dumbarton and Renfrew, before gaining the position of Chief Draughtsman with Scott & Linton at Dumbarton, where he worked on their noted clipper Cutty Sark under Hercules Linton (1831 - 1900). Rennie was appointed Naval Constructor and Instructor for the Chinese Government, working in Shanghai. This was a position he occupied for 8 years. He returned to Scotland, working principally with the Ardrossan Dry Dock and Shipbuilding Company and then, for 19 years, with John Fullarton & Company at Paisley. During his career Rennie also designed various instruments used in ship-building.