Pascoe St Leger Grenfell (1798–1879) was a British businessman and patron, and a key backer  of the South Australian Company. He was a committee member of the South Australian Church Society, and is known for donation of an acre of land on North Terrace, Adelaide which was used for the construction of the Holy Trinity Church — one of the first churches built in the city and the colony. He also donated 40 acres of land for the use of the church as glebe lands. This land later became the suburb of Trinity Gardens. Grenfell Street, Adelaide was named after him.
Pascoe St Leger was the second son of Pascoe Grenfell (1761–1838) and Georgiana St Leger and grandson of Pascoe Grenfell (1729–1810) and St Leger St Leger, 1st Viscount Doneraile. He was born 5 November 1798 in London, died 27 March 1879 in Nottingham, and was buried in the family vault in Taplow, Buckinghamshire. He was schooled at Eton College. He married twice, having 9 children by his first wife, one of whom was Field Marshal Francis Grenfell, 1st Baron Grenfell.
Following the death of his father in 1838, Grenfell took control of Pascoe Grenfell & Sons, his father's and grandfather's copper and tin smelting businesses on the River Tawe, Swansea, Wales. On the abolition of slavery by Britain in 1833, Grenfell applied for compensation for the 347 slaves he owned in Jamaica.
Pascoe St Leger Grenfell along with another South Australia Company Director Raikes Currie, William Wolryche-Whitmore and Reverend Sir Henry Robert Dukinfield were key committee members of the Society for the Propagation of the Gospel in Foreign Parts (SPG) and were all involved with the establishment of South Australia as a free colony. In the mid 1830s Grenfell was involved with the South Australian Church Society, an organisation primed to generate funds for the construction of churches and employ ministers in the new colony of South Australia. Colonel William Light, the Surveyor General of the new colony and the City of Adelaide, had authority to select land for the South Australian Church Society. He selected the site where Holy Trinity Church stands on North Terrace. Pascoe St Leger Grenfell transferred Town Acre No. 9 (order no. 171) for the building of the Holy Trinity Church, Adelaide and 40 acres of country land for 'glebe' lands in an area that later became the suburb Trinity Gardens. Grenfell had purchased the land in December 1835 for 12 shillings but by March 1836 had donated it for the church. The entire donation had an estimated value of 70 shillings and made him the largest private contributor to the venture.