British naturalist and missionary from Stradbroke, Suffolk. He accompanied Capt. F.W. Beechey as naturalist on his voyage in HMS Blossom (1825-1828) exploring in the Pacific. The primary purpose of the expedition was to act as a relief and support vessel to John Franklin's second arctic expedition in search of the north-west passage, but Franklin's expedition had to turn back and the Beechey expedition's main contributions were made elsewhere in the region. Plant collections from Beechey's expedition were made by Lay and A. Collie, the specimens being subsequently worked on by W.J. Hooker and G.A.W. Arnott (1799-1868) over a period of many years.

Beechey surveyed Bonin islands (1827) where he formally took possession of them, leaving a copper plaque declaring his claim in respect of Great Britain nailed to a tree. Later, returning to China as a missionary for the British and Foreign Bible Society (1833-), Lay published on trade opportunities with region and in an open letter (1836) to the british public, urging occupation of the Bonin Islands declaring that "this spot might, under the blessing of the Almighty, be the focus from whence the influences of religion, science, and the sentiments of political freedom, would emanate in an ever-flowing tide".

Lay continued to work in the region, acting in both a religious and political capacity, visiting Brunei in 1837 and publishing and account of the Chinese people in 1841. He became first British Consul at Fuzhou (1844) when it was opened to foreign trade in under the Treaty of Nanjing which concluded the recent Opium War (1839-1842) between Birtain and China. Lay continued to send specimens from China back to Hooker who acknowledge his contribution to science with the genus Layia Hook. & Arn.. Hooker later erroneously published the same name for a genus in the Fabaceae, but this name has since been formally rejected.