The former deputy leader said in a TV interview yesterday that it was “a bit of a mystery” to her why she failed to put herself forward for the role when Gordon Brown resigned in 2010.
Ms Harman also said Mr Corbyn needed to do more to encourage women into leadership roles, saying “it can’t carry on raining men” within the Labour Party.
Asked whether she wished she had stood for leader, Ms Harman said: “In a way I do and I think the moment I should have run is in 2010 when Gordon [Brown] stood down. It sort of took everybody by surprise as we all thought he would stay and hand over.
“Then I became acting leader and suddenly realised I could do it, so at that moment I should have stepped forward and it is a bit of a mystery to me why I didn’t. But I think the world is full of men who aren’t up to the job pushing themselves forward, and loads of women who are up to the job who don’t, and for that moment I was probably one of them.”
She said the shortage of women in top roles was a problem for Labour, which prides itself on being the party of equality.
Ms Harman said: “It is a paradox. If I knew what the problem was and we could just throw a switch and change it – but certainly more and more people are beginning to recognise that it just looks downright old-fashioned to think that men have to make the decisions and women have to abide by them.”
The MP said: “It is down to all of us to say it can’t just carry on raining men in the Labour Party. Men at the top have got to share power with women. That hasn’t happened yet but it has got to. It is part of really changing Labour to make us the modern progressive party we ought to be.”
Pressed on whether Mr Corbyn needed to do more, she said: “We should be doing more to make sure this equality happens; of course he should be, we all should be.”
Ms Harman also said Labour was not mounting an effective opposition, as it lacked public support.
She said: “I think you can’t be an effective opposition if you haven’t got enough public support because the government doesn’t need to worry about you, they only look at their own side. They don’t need to be concerned about us.
“We do need more public support in order to be an effective opposition, let alone a credible alternative government. We certainly have work to do.”