Ernest Augustus Runtz was born in 1859, the sixth son of John J Runtz of Stoke Newington. A brother, Sir John Johnson Runtz, later joined their father's insurance broking firm as J J Runtz & Son, and was a member of the City Corporation from 1908 and first mayor of Stoke Newington in 1900. Ernest Augustus was articled to Samuel Walker, a London architect and chartered surveyor, from 1875 to 1880. Then three years later in 1883, he was taken into partnership. By 1889 Runtz had decided to extend the practice into architecture and began taking Professor Roger Smith's classes at University College when he won the Donaldson Silver Medal for Fine Art. He subsequently spent two years with Frederic Richard Farrow, then secretary of the Architectural Association, and while with Farrow, passed the qualifying exam, He was, however, refused admission as ARIBA because of his partnership with Walker which he dissolved on 1 January 1897 in an initially unsuccessful attempt to resolve the matter; he remained temporarily in the same office at 22 Moorgate Street after the dissolution of the partnership.
Runtz then recommenced practice as an architect in partnership with Albert Charles Breden, although it is unclear what the practice title was thereafter: there is evidence for it becoming Ernest Runtz & Co [Earl & Sell], whilst in 'Academy Architecture' it appears simply as 'Ernest Runtz'. Born about 1864, Breden had been articled to Benjamin Woollard about 1879-83, had studied at South Kensington and had spent a period as improver with Theophilus Allen in 1884. He was then successively assistant to Augustus Frere, Thomas Mullet Ellis, Edward Dru Drury & Alfred Lovejoy and the Veritys before joining Runtz. While an assistant he had passed the qualifying exam and was admitted ARIBA on 13 June 1892, his proposers being Frere, Drury and the London architect and surveyor Benjamin Tabberer.
Runtz was one of those selected to compete for the Strand-Aldwych improvements in 1900. Breden died on 12 January 1903, and Runtz then took George McLean Ford into partnership, the practice title becoming Ernest Runtz & Ford from that year. Born in 1867, Ford had been articled to Shiells & Thomson in Edinburgh 1884-89, and had spent about a year as assistant to James Bow Dunn before moving to London as assistant to John Birch. This enabled him to study at South Kensington and the Architectural Association and pass the qualifying exam in 1892. He was admitted ARIBA on 21 November 1892, his proposers being Leonard Aloysius Stokes, Arthur Cates and Edward Augustus Gruning.
Runtz had a very large commercial and theatre practice, mostly in a neo-Baroque style, influenced mainly by Belcher and Pite, but with continental nuances. His theatres were much admired by Edwin O Sachs in 'Modern Opera Houses and Theatres' but more recent opinion has been critical. The RIBA relented on the issue of his membership in June 1908 when he was admitted FRIBA, his proposers being John MacVicar Anderson, Aston Webb and Charles Henry Brodie.
Runtz was the most high-profile casualty of the Finance Act of 1909 which, as he himself observed, had made 'real property an unpopular and uncertain investment', but his financial problems had begun several years earlier. From 1897 until 1906 his earnings from his practice had averaged £2,500 to £3,000 per annum, but in 1907 the Law Guarantee & Accident Society failed, resulting in a loss of £600 per annum in fees. In 1908 he had to resign from the board of the Birkbeck Bank, of which he had been a director since 1888, 'as a consequence of his losing an action brought by him as trustee against the other directors'. This resulted in his losing a further £600 per annum and incurring legal costs. Runtz's practice had several significant commissions in 1908, but in the following year a second major client, the New London Discount Company, failed, apparently owing significant sums, and on 7 September Ford withdrew from the partnership which was to show a loss of £406 for that year. Runtz took his son Ernest Munro Runtz into partnership as E Runtz & Son, and the practice returned to profit in 1911 when it made £683. During these late years he and his son sometimes worked in association with Farrow's practice.
In 1912 Runtz had to have an operation, having been in poor health for at least a year. Although he had no other income, his wife's London East End properties having produced no rental since 1910, Runtz retired from the practice, probably with the object of insulating both it and his son from his rapidly mounting financial difficulties. A judgment against him for £600 resulted in him becoming bankrupt on his own application on 3 April 1912, his debts amounting to £8,387 15s 2d and his assets £505 5s 3d.
In January 1913 Runtz's discharge from bankruptcy was suspended for the minimum period of two years. He did not live that long, dying on 15 October from the after-effects of the operation of the previous year.