Baer was set to retire at the end of the year as he would have reached the court's mandatory retirement age of 75. He was sworn in as chief justice last year and was first elected to the state's high court in 2003, as a Democrat.
"Pennsylvania has lost a jurist who served the Court and the citizens of the Commonwealth with distinction," said fellow Supreme Court Justice Debra Todd.
"Chief Justice Baer was an influential and intellectual jurist whose unwavering focus was on administering fair and balanced justice. He was a tireless champion for children, devoted to protecting and providing for our youngest and most vulnerable citizens."
According to the Supreme Court, Todd, the longest-serving jurist on the panel and a Democrat, now succeeds Baer as Pennsylvania's first female chief justice.
Baer's death leaves a 4-2 Democratic majority on the Supreme Court. According to the court, his seat was already set for the 2023 ballot, though the governor may make an appointment in the interim, which would then be confirmed by the state Senate.
A Pittsburgh native, Baer graduated from the University of Pittsburgh in 1971 and Duquesne Law School in 1975. He served as Pennsylvania's deputy attorney general from 1975 to 1980.
After spending much of the following decade in private practice, he was elected to Allegheny County's Court of Common Pleas in 1989. Four years later, he was appointed to the county's family court as an administrative judge.
Gov. Tom Wolf offered his condolences as well, saying, "I'm extremely saddened to learn that Chief Justice Baer passed away. He was a respected and esteemed jurist with decades of service to our courts and our commonwealth. I am grateful for his contributions and leadership in the Supreme Court." Wolf ordered the state's flag lowered to half-staff immediately at all state facilities, public buildings and grounds.
"The duties of a constitutional office are heavy and the legal issues that Chief Justice Bear decided over many years were not simple or easy," said state House Speaker Bryan Cutler. "The chief justice was an honorable man doing a difficult job. He was respectful, honest and carried himself with dignity and integrity. Those are all the hallmark qualities of a true public servant, regardless of title or position."
Baer was recognized on several occasions for his advocacy on behalf of children, including being named Pennsylvania's Adoption Advocate of the Year in 1997. Among other honors, he was given the U.S. Department of Health and Human Services' Adoption 2002 Award for Judicial Innovaton in 1998 and named Child Advocate of the Year in 2000 by the Pennsylvania Bar Association.
"Since becoming a Supreme Court Justice in 2003, he worked to implement further reform to Pennsylvania’s courts and child welfare system, reducing the number of children in foster care and the length of time a child spends there, and earning national recognition for Pennsylvania’s child welfare system," said Wesley R. Payne IV, chancellor of the Philadelphia Bar Association.
State House Majority Leader Kerry Benninghoff recognized his focus on Pennsylvania's children. "His admirable work in the area of foster care, adoption and child advocacy is something that has had a monumental impact on the lives of countless Pennsylvania children and made the dream of becoming a family a reality for many," he said.
The Associated Press contributed to this story.