Is he right?
There were 306,000 UK-born people with residency in Spain in 2015, according to the European statistics agency Eurostat, which used figures reported by Spanish authorities.
The number of UK citizens living in Spain in the same year was very similar, at almost 302,000, according to the same source.
The number of Brits living in Spain was higher before the financial crisis hit - more than 351,000 in 2008 - but has never been nearly as high as the 750,000 that Mr Corbyn claims. If you take into account people who spend part of the year there, the figure is certainly higher, but there are no reliable, up-to-date statistics available on that.
Around one-third of Brits resident in Spain receive the UK state pension.
Two million British people living in other parts of Europe is a huge exaggeration, even if he meant to include Spain. The UN estimated that there were 1.2 million UK-born people living in other EU countries, including Spain, in 2015. That figure is based on the 2011 census.
If you take into account UK-born people who spend part of the year in another EU country, the figure is certainly higher, although there are no up-to-date estimates of this.
A 2010 study, published by The Institute for Public Policy Research (IPPR), suggested there were 1,050,000 UK citizens living in Spain for at least part of the year. . The study was used in the answer to a parliamentary question on the number of Brits living abroad in 2014.
In 2006, the BBC News website said there were 761,000 Britons resident in Spain, using even older IPPR research. These figures are out of date now and the IPPR itself no longer uses them.  The think tank takes the UN figures and says on its website: "approximately 1.2 million Britons live in other EU countries - mainly in Spain, Ireland, France and Germany."
Reality check verdict: Wrong - the real figure for UK-born residents of Spain is 306,000, and for the EU as a whole is 1.2 million.
Read more: The facts behind claims in the EU debate
In his first speech on the EU Referendum, Jeremy Corbyn said: "There are nearly three-quarters of a million British people living in Spain and over two million living in other parts of Europe."