Savills, founded in 1855, is part of a group of investors who have put fresh funding into the rapidly growing web-based estate agency market.
Industry experts estimate 5% of UK homes a year are currently sold through hybrid estate agencies - around 50,000 properties - and predict that internet-based firms like YOPA could handle up to 50% of all sales by 2020.
YOPA says it brings together the expertise of a dedicated local estate agent to guide buyers and sellers through a sale, combined with the cost-saving efficiency of an online service.
The hybrid firm operates with a growing network of local estate agents across the UK, and allows people to sell their property for a fixed fee of £780.
Daniel Attia, co-founder and chief executive of YOPA, said: "Savills is the UK's leading brand in property services with substantial global operations and is known for its entrepreneurial spirit and commitment to innovation."
Savills chief executive Jeremy Helsby added: "We have followed the rapid advance of the online hybrid estate agency model over the last year.
"This investment broadens the group's access to the UK residential sector by enabling us to take an interest in the high volume segment of the market, comprising over one million transactions annually, to which Savills has had little exposure to date."
Savills' funding came through its investment arm, Grosvenor Hill Ventures. Other investors include Andrew and Alistair Barclay, who are members of YOPA's founding team, and are related to business moguls Sir David and Sir Frederick Barclay.