The firm was established in 1822 when William Henry Ashurst set up practice as a solicitor at 2 Sambrook Court, Basinghall Street, London. In 1823, he went into partnership with William Henry Green under the name 'Green and Ashurst'. The partnership lasted until 1829, when Ashurst moved to 84 Newgate Street to practise alone. In 1835, Ernest Barnevelt Elliott Gainsford became a partner and the new partnership 'Ashurst and Gainsford' set up office at 137 Cheapside. However, the partnership only lasted five years, and Ashurst once again practised alone, significantly spending a year as solicitor to the Mercantile Committee helping Rowland Hill succeed in reforming the postal system. In 1843, Ashurst decided to make his son William Henry Ashurst Junior a partner under the style 'Ashurst and Son'. The firm moved to 6 Old Jewry in 1854 and remained there until 1890. In 1864 John Morris, who had worked for Ashurst and Son for many years, became a partner and the firm changed its title to 'Ashurst and Morris'.
In the 1860s, the firm's title was altered to 'Ashurst Morris and Company' when partnerships were forged with Thomas Norton Harvey between 1865 and 1877 and George Davis from 1869 to 1874. Frank Crisp became a partner in 1871 and in 1877 the firm adopted the title 'Ashurst Morris Crisp and Company'.
In 2003, to keep in line with competitors, Ashurst Morris Crisp was rebranded as 'Ashurst LLP'. A merger with Blake Dawson in 2012 saw the firm become the 25th largest in the world with 24 offices in 14 countries.