The lender launched its first products on January 9 and has received more than 850 applications from brokers since that date.
The first deal was completed by a broker at Your Move who agreed a two-year fix at 4.99% with the lender.
Brad Fordham, managing director of Santander for Intermediaries, said: “There’s been a huge response to our new Help to Buy products, with over 850 applications already in the pipeline, so it’s great to be announcing our first completion so soon – in just three weeks – with many more to come.
Earlier today Santander revealed 2013 gross lending reached £18.4bn, a £4bn rise on the previous year.
“Santander for Intermediaries is focused on offering great service and writing quality business, helping our intermediary partners help their clients,” Fordham added.
“These latest developments, coupled with our year-end figures which has seen an increase of almost £4.5bn in our mortgage lending, should make it clear that we’re open for business.”