SYDNEY, Australia — For decades she has blazed a trail in the Australian media, bringing the news to homes around the country. But on Monday, Lisa Wilkinson herself became the subject of the day’s breaking news, her resignation reigniting a fierce debate about a gender pay gap, an issue that has increasingly roiled the media industry.

“I’m sad to say that today was my last day on ‘The Today Show,’” Ms. Wilkinson wrote on Twitter late Monday, referring to Nine Network’s flagship breakfast program, which she had co-hosted for a decade.

Her post contained a statement from the network confirming the split, which came after months of contract negotiations. “We have been unable to meet the expectations of Lisa Wilkinson and her manager on a contract renewal for a further period,” the network statement said, adding that it was “disappointed we find ourselves in this position.”

News of her abrupt departure set off speculation that Ms. Wilkinson, 57, had quit over an equal pay dispute. She had for 10 years been a co-host alongside Karl Stefanovic and at times had fended off questions about a pay gap between the two.