Gov. Tom Corbett, U.S. Sen. Bob Casey and state Supreme Court Chief Justice Ronald Castille were among about 600 people who crowded into the Capitol rotunda and cheered as Kane finished taking her oath.
In a speech, the 46-year-old Kane pledged to protect Pennsylvanians against violent criminals, child molesters, scam artists and others who would do them harm.
"You will see the Office of Attorney General take a leadership role on the front lines - aggressive, efficient and mission-focused," she said in her first speech as the state's chief legal officer, a position in which she'll oversee 700 employees, including 180 attorneys.
Kane was among three statewide Democratic officers who were sworn in Tuesday in back-to-back ceremonies at different locations in the Capitol complex.
Eugene DePasquale, a former state representative from York, took the oath as auditor general, and Rob McCord was sworn in to his second term as state treasurer.
All three will serve a four-year term and receive the same salary, currently $155,797.
The attorney general was appointed by the governor until it became an elective post in 1980. Until Kane's election, it was held by a procession of male Republicans.
"It's just an historic occasion," Castille said as he waited in a front-row seat for the ceremony to begin.
Kane, who spent nearly 13 years as a Lackawanna County prosecutor, left that office in 2007 to work on Hillary Clinton's campaign for president.
She defeated former U.S. Rep. Patrick Murphy in the April primary in a $2 million-plus campaign financed mostly by her husband Chris, a co-owner of his family's trucking and warehousing company. He and their two sons accompanied Kane to Tuesday's ceremony.
In the general-election campaign, Kane ran on her promise to investigate the handling of the Jerry Sandusky child sexual abuse scandal to find out why it took state investigators nearly three years to arrest the former Penn State assistant football coach.
Corbett, a Republican, was the attorney general during most of that period, including his 2010 campaign for governor. He has defended the pace of the investigation and cited Sandusky's conviction on 45 counts as evidence of its success.
As Kane arrived in the rotunda Tuesday, Corbett stood and shook her hand.
In recent days, Kane has said she intends to appoint a special deputy attorney general to focus solely on the investigation and promised to make those findings public.
Kane succeeded Linda Kelly, whom Corbett appointed to finish his term as attorney general once he was sworn in as governor. Kelly promised up front not to seek a full term.
DePasquale, speaking at his ceremony at the Pennsylvania State Museum next to the Capitol, vowed to conduct an audit to ensure that the Department of Environmental Protection has adequate resources to protect water supplies from being polluted by drilling in the state's fast-growing natural gas industry.
As the state's fiscal watchdog, DePasquale said he wants to use his auditing power to shape "workable solutions" to make the state government work better.
DePasquale, 41, who worked in the DEP during the Rendell administration, served six years in the state House of Representatives. He succeeds fellow Democrat Jack Wagner, who had served the maximum two terms, as auditor general.
McCord, 53, a former venture capitalist, said his leadership as treasurer has produced $1.6 billion in investment returns and averted hundreds of millions of dollars in wasteful spending during his first term.
"I want to make government work smarter and more efficiently. I also want to promote the idea of return-oriented public investments," he said.