Speaking from the party's conference in Brighton, the member for East Ham said he didn't anticipate so many people seeing the new leader as someone who speaks for them.
"Jeremy is onto something very important here that thousands and thousands of people have recognised in him someone who can speak for them.
"He's given them the sense that politics, for the first time in many cases, is something worth being involved with."
Mr Timms also said he was delighted so many people had joined Labour since the election.
"What's great especially is to see so many young people joining the party for the first time. We've had a real struggle in getting young people to vote in general elections. I think that's a very important and very welcome change that Jeremy has succeeded in bringing about.
"The most extraordinary thing that's happened since the general election is that our party has more or less doubled in size."
Jeremy Corbyn will deliver his leader's speech at the conference on Tuesday.
Listen to Stephen Timms speaking to Premier's Political Editor Martyn Eden: