Morgan was selected by Cardiff North Labour Party as their candidate for the 1992 general election.

She became the first woman to represent a Cardiff constituency and, at the time of her election, was one of only four women MPs from Wales.

Morgan made her maiden speech in Parliament on 22 May 1997 in the debate on the Referendums (Scotland and Wales) Bill, designed to pave the way for devolution.

Commentators ascribed her victory to a strong personal vote, decisive in a campaign dominated by issues such as the Iraq War, criticism of Tony Blair and a leap in council tax caused by periodic revaluation of property values.

[11] During her second term, she opposed variable tuition fees for university students, citing fears that it would open up a market in higher education.

Nevertheless, her voting record is supportive of the Labour Government, until it proposes a measure she cannot reconcile with her fundamental beliefs—such as the equal treatment of children, for instance in the asylum system, or in respect of protection from violence.

Morgan has been involved in the field of women's rights (having heavily promoted the introduction of all-women shortlists for political parties), as well as the welfare of children, black and minority ethnic and disabled people.

She was one of the founders of the Purple Plaques scheme of public markers for remarkable women who lived in Wales.