Governor Deval Patrick is slated to announce Thursday that nearly half of his Cabinet is being replaced as he begins the final two years of his second term, and that Suffolk County Sheriff Andrea Cabral will join his administration as the state’s public safety secretary, a variety of people briefed on the changes confirmed to the Globe.

Administration and Finance Secretary Jay Gonzalez, as well as Health and Human Services Secretary Dr. JudyAnn Bigby, Public Safety and Security Secretary Mary Beth Heffernan, and Education Secretary Paul Reville are all departing the administration, the State House insiders confirmed, requesting anonymity to speak freely before the formal announcement.

Gonzalez will be replaced by Glen Shor, who was a top deputy before leaving the secretariat in June 2010 to run the state’s health insurance connector program.

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Bigby will be replaced by John Polanowicz, currently the president of St. Elizabeth’s Hospital in Brighton, the largest Steward Health Care System hospital.

And Heffernan will be replaced by Cabral, who was initially appointed sheriff for the county that includes Boston in 2002, and is the first woman in state history to serve as sheriff. Patrick will appoint a replacement as sheriff, a coveted post with a six-year term, until a special election in 2014.

The replacement for Reville could not be immediately confirmed.

“This is a natural inflection point for the administration,” a top Patrick aide told the Globe. “All the Cabinet would stay for the next years if they could, but people are at different points in their lives and careers, so not all of them can make that commitment.”

The aide, who also requested anonymity to speak freely before the announcement, added: “What’s exciting is that the talent and the experience and the quality of the people who will be joining the Cabinet this week is exceptional. The governor has a big agenda and a lot he wants to get done next year and we’ve put together another really strong team.”

The governor told his top aides after last month’s presidential election that he wanted them to either recommit to their positions for the remainder of his term or agree to depart so he could find a replacement.

He made the same demand of his first-term Cabinet after winning reelection in November 2010, preferring continuity rather than piecemeal staff changes. The governor himself has already declared he will not seek a third term, as well as that he will not resign early to take a Cabinet appointment in the Obama administration.

Energy and Environmental Affairs Secretary Richard Sullivan; Housing and Economic Development Secretary Greg Bialecki; Elder Affairs Secretary Ann L. Hartstein; Labor and Workforce Development Secretary Joanne Goldstein; Secretary of Veterans’ Services Coleman Nee; and Transportation Secretary Richard Davey will remain in their posts.

The governor is slated to announce the staff changes during a news conference.

A spokesman refused to confirm either the news conference or its subject matter.

Patrick’s official schedule did not include it, but it is often amended with surprise announcements.