Ontario Premier Kathleen Wynne will go into the 2018 election campaign without her deputy premier and another long-serving cabinet minister, after both announced Friday they will not seek re-election.

Deputy premier Deb Matthews and Treasury Board President Liz Sandals issued statements within minutes of each other that they would not run again.

Matthews entered politics 15 years ago, winning three consecutive terms, and has held the portfolios of minister of children and youth services, minister of health and minister of advanced education and skills development.

"Ontario is a better place today than it was in 2003. I am proud to have been part of that change," Matthews wrote in a statement to the media.

Matthews said she will stay on as co-chair of the upcoming election campaign.

Sandals has been in politics for 30 years, 15 with the Liberal Party, acting as minister of education during difficult labour negotiations with the province's teachers.

Sandals said Friday she plans to retire.

Premier thanks MPPs for service

Wynne thanked Matthews and Sandals for their service and friendship, calling them both caring and compassionate people.

"Very quickly after we met, Deb and I became close friends," Wynne said in a statement.

"She has always, always supported me, which is why I completely understand, appreciate and support her decision to retire as an MPP at this time," Wynne said.

The premier said she intends to rely on Sandals' wisdom and leadership over the coming months as the election campaign kicks into high gear.

"I will miss Liz's steady hand, wise counsel and friendship. Her years of experience and strong set of values have always been a guiding light for me and our whole team," Wynne wrote in her statement.

Loss of Liberal veterans

Political observers were quick to comment on the significance of losing two high-ranking Liberals so close to an election.

"You are going to have fatigue on the front bench," said Lydia Miljan, a political science professor at the University of Windsor. She said it will be a challenge for the Wynne Liberals to sell the idea of "stability" to voters.

"[This] is a serious change in how the government will move forward and how they're going to put a face on expertise and knowledge."

Miljan also believes that Wynne will be losing a piece of the party's identity that was built around strong women at the helm.

A number of other high-ranking Liberals have chosen not to run again in 2018.

In September, Economic Development Minister Brad Duguid said he would not seek re-election, while Speaker Dave Levac, the Liberal representative for Brant, as well as Monte Kwinter, Ontario's oldest member of the legislature, also announced they will not run.

Matthews said she will "explore opportunities" for her life after provincial politics.

"As I prepare to leave elected life, I have one message," Matthews said. "Politics matter. Politicians matter. It matters who gets elected."