Diane Abbott insisted her time as a trainee civil servant would prepare her for becoming home secretary and that her views on the IRA had changed - just like her "splendid afro".
The shadow home secretary distanced herself from claims she supported the IRA in the 1980s by saying, "I don't have the same hairstyle, I don't have the same views”.
She made the comments during a bizarre interview on the Andrew Marr Show on Sunday, during which she was grilled on her stance on security following the Manchester bombing.
Labour has pledged to recruit 1,000 more staff at security and intelligence agencies MI5, MI6 and GCHQ since the attack on Monday.
Ms Abbott was challenged on her views after it emerged she had signed a parliamentary motion calling for an end to "conspiratorial groups" in 1989.
She said: "At that time, I and a lot of people felt MI5 needed reforming. It has since been reformed and of course I would not call for its abolition now."
Pressed on the issue, she said: "That MI5 has gone. It's been reformed, it's a different MI5 and that's why so many of us are able to support it now."
She defended voting against "counter-productive" counter terror legislation, which was also opposed by many senior Conservatives.
Asked about her views on the IRA in the 1980s, she said: "It was 34 years ago, I had a rather splendid afro at the time. I don't have the same hairstyle, I don't have the same views.
"It was 34 years on. The hairstyle is gone, some of the views are gone."
Ms Abbott insisted that she had worked as a graduate trainee in the Home Office so she was qualified to take on the role, which would make her the first black person to hold one of the most senior ministerial positions.
She said: "First of all, I think there's something to be said for a home secretary who has actually worked in the Home Office.
"I worked in the Home Office for nearly three years as a graduate trainee and I know how it works from the inside."
Ms Abbott, who has represented Hackney North for 30 years, said her experience working in diverse communities would help her in the role.
Home Secretary Amber Rudd shot back at Ms Abbott's comments, telling the Andrew Marr Show: "What I would say to Diane Abbott is I have changed my hairstyle a few times in 34 years as well, but I have not changed my view about how we keep the British public safe."
Labour leader Jeremy Corbyn, asked if Ms Abbott's hairstyle comments trivialised the IRA, told ITV's Peston On Sunday: "Diane's hairstyle is a matter for Diane."
Pressed on the issue, Mr Corbyn said: "We learnt, all of us, a lot from the whole experience of Northern Ireland.
"Remember what it was like... in the late 70s and early 80s, the military presence all over Northern Ireland, the huge divide between communities, the lack of any communication between communities, the idea that there'd be a military solution when we knew there wouldn't be.
"I remember arguing with many people in parliament and when Ian Paisley was thrown out of parliament for accusing the prime minister of talking to the republicans, which she denied she was and it turned out she probably was, I actually defended him on being thrown out of parliament."
