AP Photo/Kirsty Wigglesworth
But he hasn't always been supportive of being a member of the 28-nation bloc. In fact he even voted in favour of leaving the European Economic Community -the EU's predecessor- in 1975.
Speaking on Thursday morning in Central London, Corbyn urged British voters to accept the EU "warts and all."
He added, "there is a strong socialist case for staying in the European Union, just as there is also a powerful socialist case for reform and progressive change in Europe."
Polls show that the "Remain" and "Leave" campaigns are neck-and-neck and Corbyn's opinion could sway some votes.
A YouGov poll published in The Times on Thursday shows that when it comes to the EU, Corbyn - the leader of the opposition - is the most trusted British politician. Twenty-eight percent of people trust the statements and claims made by Corbyn on the EU, while only 21% trust the statements from Prime Minister David Cameron.
Despite Corbyn pushing for Britons to vote for staying within the EU, it looks like he has changed his stance over the bloc - big time.
Here's a list of some of the things Corbyn has done and said in the past that would appear to show that he is very skeptical of the EU.
- He voted in favour of leaving the European Economic Community in 1975.
- He voted against the Maastricht Treaty that created the EU. Here's what he had to say about it - "It takes us in the opposite direction of an unelected legislative body-the Commission-and, in the case of foreign policy, a policy Commission that will be, in effect, imposing foreign policy on nation states that have fought for their own democratic accountability."
- He voted against the Lisbon Treaty which is the current constitutional basis for the EU.
- Writing about the Greek crisis last year Corbyn said - "There is no future for a Europe that turns its smaller nations into colonies of debt peonage."
- In an LBC interview, Corbyn implied that the EU was treating Greece "brutally." - "If Europe becomes a totally brutal organisation that treats every one of its member states in the way that the people of Greece have been treated at the moment, then I think Europe will lose a lot of support from a lot of people."
- In an article on his website, Corbyn wrote that the EU was responsible for the gross abuse of human rights in Western Sahara. However, the article was deleted.
- In another deleted article on his website, Corbyn wrote this - "The project has always been to create a huge free-market Europe, with ever-limiting powers for national parliaments and an increasingly powerful common foreign and security policy."
- A spokesman for Corbyn said the articles were deleted because they are "converting it [the website] to reflect his work as leader and afterwards."
And finally here's a TV interview that was dug up by the pro-Brexit organisation Leave.EU. In it he says the European Union's bureaucracy is unaccountable to anybody.
Corbyn's views on the EU. pic.twitter.com/zg3kTg89N9
- LEAVE.EU (@LeaveEUOfficial) April 14, 2016
It appears Corbyn's change of heart follows closely after his election as leader of the Labour party which is overwhelmingly pro-EU. Some 213 of Labour's 231 MPs have signed up to Labour In For Britain - Labour's Remain campaign group.
Corbyn preempted criticism over his change of mind, by admitting in his speech that he has a track record of being critical of the EU. He said he remains critical, but we need to work with it to change it. Here's what he said, the added emphasis is ours.
Over the years I have continued to be critical of many decisions taken by the EU and I remain critical of its shortcomings, from its lack of democratic accountability to the institutional pressure to deregulate or privatise public services.
So Europe needs to change.
But that change can only come from working with our allies in the EU. It's perfectly possible to be critical and still be convinced we need to remain a member.