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Notes in italics from Pevsner Architectural Guides,
Edinburgh by John Gifford, Colin McWilliam and David Walker (1991), Yale University Press.

The Church is famous for its elliptical plan which was the first in Britain. Designed by Major Andrew Frazer of the Royal Engineers, 1782-4. The 51 m. steeple, probably also designed by Frazer, was built by Alexander Stevens in 1787. ... To this simple droved masonry form is attached a tetrastyle Corinthian portico of smooth ashlar, raised on only a couple of steps so that the columns stand practically on the same level as the life of the street. Columns, mouldings and steps are of Craigleith, the ashlar of Redhall stone. The steeple stands well on the portico but is decidedly less original, the spire and splayed middle stage being obviously Gibbsian.
Inside, the oval plan is complemented by the ceiling (concentric ovals surrounded by husk garlands) and by the curving panelled gallery (with original pews) on Roman Ionic columns. ...