Dianne Abbott has said she no longer opposed the security services as Labour pledged to recruit 1,000 more staff at M15, MI6 and GCHQ to step up efforts to prevent terrorism.
She also tried to distance herself from claims she supported the IRA in the 1980s.
Asked about comments she made back then, 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."
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 told Marr: "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."
Ms Abbott, who has represented Hackney North for 30 years, said her experience working in diverse communities would also help if she were to become home secretary.
If Ms Abbott was given the job if Labour won the General Election she would be the first black person to hold one of the most senior ministerial positions.
The Shadow home secretary, 63, told The Andrew Marr Show: "I think there's something to be said for a home secretary who's 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."
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."
Asked if Ms Abbott would be his home secretary, Mr Corbyn appeared to misspeak as he replied: "Diane is our home affairs spokesperson and I'm looking to appoint our shadow cabinet."
Home Secretary Amber Rudd shot back at Ms Abbott's comments, telling the 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."