Belinda Stronach said Thursday that she's leaving politics to fulfill a commitment to her family business -- not because she's tired of public service.

"I still have a very keen interest in public service and in public policies and the issues that impact us all greatly, so it's not for lack of interest and enthusiasm that I'm departing at this stage," she told CTV's Canada AM.

"It's a commitment really at the end of the day to my family and to the family business."

Stronach is expected to serve as executive vice-chair of Magna International Inc., one of the top auto parts manufacturers. Her father, Frank Stronach, is Magna's founder and chairman.

She will return as Magna considers a bid for troubled auto maker DaimlerChrysler AG.

Stronach said she first started thinking about the move around Christmas when her father spoke to her about coming back to Magna.

"My immediate reaction was that I'm very committed to public life ... so this was a real tough decision for me," she said.

Stronach also said the decision to leave politics will allow her to spend more time with her children.

The 40-year-old said she will remain with her party until the next election, when a new Liberal candidate will be chosen to run for her Ontario riding of Newmarket-Aurora.

Several Liberals have chosen not to seek re-election, including former cabinet minister Bill Graham. Stronach emphasized Wednesday that her decision had nothing to do with Stephane Dion's leadership of the party.

Most recently, Stronach had been serving as Opposition critic for Competitiveness and the New Economy.

Stronach formally entered politics by running for the Conservative party leadership in January 2004. Before then, she was credited with helping to create the Conservative Party, by urging the leaders of the Reform and Progressive Conservatives to unite.

A little more than a year later, in May 2005, Stronach crossed the floor in favour of the Liberals just before a crucial budget vote that could have toppled the Liberals.

Under the leadership of then-prime minister Paul Martin, she became Minister of Human Resources and Skills Development, as well as Minister responsible for Democratic Renewal and Minister responsible for Service Canada.

Stronach's personal life came under the spotlight at the time of her defection, with her public breakup with Conservative MP Peter MacKay.

Stronach later was linked to former Toronto Maple Leaf Tie Domi as the alleged "other woman" in Domi's acrimonious divorce.