John Gilbert Baker FRS (13 January 1834 – 16 August 1920) was an English botanist. His son was the botanist Edmund Gilbert Baker (1864–1949).
Baker was born in Guisborough, the son of John and Mary (nêe Gilbert) Baker and died in Kew.
He was educated at Quaker schools at Ackworth School and Bootham School, York.
He then worked at the library and herbarium of Royal Botanic Gardens, Kew between 1866 and 1899, and was keeper of the herbarium from 1890 to 1899. He wrote handbooks on many plant groups, including Amaryllidaceae, Bromeliaceae, Iridaceae, Liliaceae, and ferns. His published works include Flora of Mauritius and the Seychelles (1877) and Handbook of the Irideae (1892).
He married Hannah Unthank in 1860. Their son Edmund was one of twins, and his twin brother died before 1887.
John G. Baker was elected a Fellow of the Royal Society in 1878. He was awarded the Veitch Memorial Medal of the Royal Horticultural Society in 1907.