On February 15, 2006, the Toronto—Danforth NDP riding association nominated Tabuns as the party's candidate in the provincial by-election, to fill the vacancy caused by the resignation of former NDP Member of Provincial Parliament Marilyn Churley.
Churley resigned her provincial seat in order to run in the 2006 federal election as the NDP candidate for Beaches-East York.

Tabuns' opponents in the election were former broadcaster and Liberal candidate Ben Chin, Progressive Conservative candidate Georgina Blanas and Green Party candidate Paul Charbonneau.
On March 30, 2006, Tabuns won the by-election with 47.8% support from voters.

Upon being sworn in as an MPP, NDP Leader Howard Hampton reorganized his shadow cabinet and gave the rookie member a long list of portfolios, including Transportation, Environment, Public Infrastructure Renewal, Greater Toronto Area, Culture, Tourism and Recreation, Citizenship and Immigration, and Multicultural Affairs.

In October 2006, Tabuns was voted Best MPP by Now Magazine readers, for his positions on climate change, the Portlands Energy Centre, and early childhood learning centres in his constituency.
Tabuns has also been known for his stance on same-sex parental rights, anti-toxics legislation and recognition of foreign credentials.
In the same month, Tabuns was recognized for tabling a motion to recognize June 22, 2006 as Chinese Canadian Head Tax Redress Day.

Tabuns was re-elected in the 2007, 2011, 2014, and in the 2018 provincial elections.

He is currently the party's critic on energy and climate change, and was previously the party's critic for Education and Energy issues.
On February 15, 2006, the Toronto—Danforth NDP riding association nominated Tabuns as the party's candidate in the provincial by-election, to fill the vacancy caused by the resignation of former NDP Member of Provincial Parliament Marilyn Churley. Churley resigned her provincial seat in order to run in the 2006 federal election as the NDP candidate for Beaches-East York.
Tabuns' opponents in the election were former broadcaster and Liberal candidate Ben Chin, Progressive Conservative candidate Georgina Blanas and Green Party candidate Paul Charbonneau. On March 30, 2006, Tabuns won the by-election with 47.8% support from voters.
Upon being sworn in as an MPP, NDP Leader Howard Hampton reorganized his shadow cabinet and gave the rookie member a long list of portfolios, including Transportation, Environment, Public Infrastructure Renewal, Greater Toronto Area, Culture, Tourism and Recreation, Citizenship and Immigration, and Multicultural Affairs.
In October 2006, Tabuns was voted Best MPP by Now Magazine readers, for his positions on climate change, the Portlands Energy Centre, and early childhood learning centres in his constituency. Tabuns has also been known for his stance on same-sex parental rights, anti-toxics legislation and recognition of foreign credentials. In the same month, Tabuns was recognized for tabling a motion to recognize June 22, 2006 as Chinese Canadian Head Tax Redress Day.
Tabuns was re-elected in the 2007, 2011, 2014, and in the 2018 provincial elections.
He is currently the party's critic on energy and climate change, and was previously the party's critic for Education and Energy issues.
Peter Tabuns