Irene R. Mathyssen (born August 16, 1951 in London, Ontario) is a Canadian politician and a Member of Parliament in the Canadian House of Commons. She was previously a New Democratic Party Member of Provincial Parliament (MPP) from 1990 to 1995, and briefly served as a minister in the government of Bob Rae.

Mathyssen was educated at the University of Western Ontario from 1970 to 1975, received a Bachelor of Arts degree in English and Drama, and a Bachelor of Education degree. She subsequently worked as an English teacher. She was a member of the London Board of Education from 1981 to 1990, and was president of the Middlesex NDP riding association from 1989 to 1990. She has long been involved in labour activism in the London region.

She was elected to the Legislative Assembly of Ontario in the provincial election of 1990, defeating incumbent Liberal Doug Reycraft by 520 votes in Middlesex. She served as government Whip from 1990 to 1991, and was a parliamentary assistant from 1991 to 1994. She was named a Minister without Portfolio, responsible for Culture, Tourism and Recreation, on October 21, 1994, near the end of the Rae government's term in office.

The NDP were defeated in the 1995 provincial election and Mathyssen was personally defeated in Middlesex, finishing third behind Reycroft and Progressive Conservative Bruce Smith.

She ran for the federal New Democratic Party in the 1997 election, and finished third in the riding of London—Fanshawe, well behind Liberal incumbent Pat O'Brien. She ran in the same riding in the 1999 provincial election and again finished third, behind PC candidate Frank Mazzilli and Liberal Peter Mancini.

Mathyssen ran in London—Fanshawe for a third time in the 2003 provincial election and this time finished a strong second, losing to Liberal Khalil Ramal by fewer than 2,000 votes.

Notwithstanding her previous defeats, Mathyssen was considered to have a strong chance of defeating Pat O'Brien in the 2004 federal election. A late surge in Liberal support, however, gave O'Brien a victory of more than 3,000 votes.

She again ran in London—Fanshawe in the 2006 election. Pat O'Brien had left the Liberal Party by this time, and sat out his remaining time in the House of Commons as an independent. He opted not to run in the 2006 election. Mathyssen won the riding with 34% of the vote becoming one of 29 New Democrats elected .

Until her election in 2006, she continued to teach English at Sir Frederick Banting Secondary School in London, Ontario and served on the District 11 Ontario Secondary Schools Teachers Federation Political Action Committee. She was a vocal opponent of the Invasion of Iraq in 2003, and has participated in many local peace rallies. Mathyssen is also a member of the Ontario Health Coalition.

Mathyssen is the chair of the NDP Women’s Caucus. At 41%, the NDP caucus has the largest percentage of women of any in the House of Commons. Mathyssen is also the NDP critic for Housing and for the Status of Women and the vice-chair of the Standing Committee on the Status of Women.

In the House of Commons, Mathyssen has tabled a Private Members Bill known as the housing bill of rights that would provide for secure, accessible and affordable housing for Canadians. She has also fought cuts to housing programs and women’s organizations and managed to secure some reinvestment in both.

Mathyssen is a committed community activist she has been involved in the Pride and the London AIDS walk, the Women’s Community House, the London Coalition Against Pesticides and the Coalition of Canadian Immigrants.

During a parliamentary session on December 5, 2007, Mathyssen stood in the Assembly and accused Conservative James Moore of looking at images of "scantily clad" women on his personal laptop computer at his desk in the House of Commons. She openly questioned his integrity and said his actions "disrespected women". James Moore denied the allegations were true. Later in the day, Mathyssen and Moore spoke in person about the incident in which Moore explained that the woman he had been looking at on his laptop computer screen was his girlfriend. Mathyssen accepted the explanation and offered her apologies.