Wallage also was active as a political activist and was one of the student leaders of the New Left movement which aimed to steer the Labour Party more to social democracy.

Wallage was elected as a Member of the House of Representatives after the election of 1982, taking office on 10 June 1981 serving as a frontbencher chairing the parliamentary committee for Science Policy and spokesperson for Education, Social Work, Equality, Minorities and deputy spokesperson for Welfare and Culture.

After the election of 1989 Wallage was appointed as State Secretary for Education and Sciences in the Cabinet Lubbers III, taking office on 7 November 1989.

Wallage was appointed as State Secretary for Social Affairs and Employment following the resignation of Elske ter Veld, taking office on 9 June 1993.

Wallage semi-retired from national politics and became active in the private sector and public sector and occupied numerous seats as a corporate director and nonprofit director on several boards of directors and supervisory boards (PostNL, International Institute of Social History, Groninger Museum, International Cycling Film Festival, Radio Netherlands Worldwide, Electronic Commerce Platform [nl], Royal Association of Shipowners and the Maritime Research Institute) and served on several state commissions and councils on behalf of the government (Council for Public Administration [nl], Accreditation Council, Kadaster and Public Pension Funds APB).