Megalosaurus was named by Parkinson (1822) [A nomen nudum in this publication. Name ascribed to Buckland and Conybeare in Buckland 1824, p. 391, Pl. 40–47.]. It is the type genus of Megalosaurinidae, Megalosaurinae, Megalosauri, Megalosauridae.

It was considered a nomen dubium by Allain and Chure (2002).

It was assigned to Enaliosauri by Parkinson (1822); to Ameivoidea by Fitzinger (1826); to Lacertilia by Owen (1841); to Megalosauri by Fitzinger (1843); to Pachypodes by Meyer (1845); to Dinosauria by Owen (1842) and Quenstedt (1852); to Dinosauria by Pictet (1853); to Deinosauria by Mantell (1854); to Harpagosauria by Haeckel (1866); to Dinosaurii by Quenstedt (1867); to Goniopoda by Cope (1869); to Theropoda by Quenstedt (1882); to Goniopoda by Cope (1866) and Cope (1887); to Dinosauria by Owen (1854), Owen (1857), Owen (1859), Owen (1860), Owen (1861), Lennier (1870), Seeley (1881), Lydekker (1883), Lydekker (1887) and Mansel-Pleydell (1888); to Megalosaurinidae by Lydekker (1888); to Megalosauridae by Nopcsa (1901); to Theropoda by Dollo (1885), Gadow (1898) and Gadow (1901); to Theropoda by Winkler (1893), Sauvage (1896), Gadow (1897), Sauvage (1914) and Joleaud (1922); to Carnosauria by Kuhn (1939); to Megalosauroidea by Haubold (1971) and Haubold (1974); to Megalosauridae by Gardiner (1982); to Carnosauria by Delair (1973) and Zhao (1983); to Carnosauria by Molnar et al. (1990); to Megalosauroidea by Holtz (1995); to Tetanurae by Holtz (1994) and Holtz (2000); to Eustreptospondylidae by Mateus (2006); to Averostra by Benson et al. (2008); to Megalosauridae by d'Orbigny (1849), Gervais (1853), Gervais (1859), Huxley (1870), Sauvage (1882), Marsh (1882), Vetter (1884), Dollo (1884), Marsh (1884), Marsh (1884), Marsh (1885), Lydekker (1885), Zittel (1890), Baur (1891), Sauvage (1895), Marsh (1895), Marsh (1896), Sauvage (1898), Van Den Broeck (1900), Sauvage (1900), Mansel-Pleydell (1902), Hay (1902), Williston (1905), Lambe (1905), Arldt (1909), Huene (1909), von Zittel (1911), Matthew and Brown (1922), Piveteau (1923), Huene (1923), Lull (1924), Depéret and Savornin (1925), Piveteau (1926), Huene (1926), Huene (1927), Depéret and Savornin (1928), Rama Rao (1932), Stromer (1934), Stromer (1934), Swinton (1936), Romer (1956), Bataller (1960), Delair (1960), Tatarinov (1964), Walker (1964), del Corro (1966), Romer (1966), Charig (1967), Steel (1970), Swinton (1970), Waldman (1974), Galton (1977), Madsen and Miller (1979), Molnar (1980), Santafé et al. (1982), Buscalioni and Sanz (1984), Welles (1984), Chabli (1986), Carroll (1988), Kurzanov (1989), Bakker et al. (1992), Currie and Zhao (1994), Holtz (1996), Gao (1999), Benson and Barrett (2009), Vila et al. (2011), Hanson and Makovicky (2013) and Hendrickx and Mateus (2014); and to Megalosaurinae by Nopcsa (1928), Paul (1988), Holtz et al. (2004), Carrano et al. (2012), Rauhut et al. (2016) and Rauhut et al. (2018).