The former state treasurer and auditor general ran as a moderate who put the interests of this diverse state ahead of party leaders. Casey had supported President Barack Obama's signature policies, including his sweeping health care law, economic stimulus bill and overhaul of financial-sector regulations.
He also supported bailouts of banks and the American automakers, borrowing authorizations to avert a national default, tougher pollution standards on coal-fired power plants, higher income taxes on higher earners and an increase in the minimum wage.
Casey had attacked Smith as too extreme for Pennsylvania, and won nearly every endorsement from the state's newspaper editorial pages.
Smith hewed closely to Republican Party-line positions, but had signaled that on key fiscal issues he would lean to the conservative side of party leaders in Congress, as well as GOP presidential nominee Mitt Romney.
Smith attacked Casey as a do-nothing career politician, the right hand of Obama and an overreaching and overspending government that is stifling entrepreneurship and the development of fossil fuels such as coal.
The campaign was Smith's first statewide after many years of giving heavily to Republican causes while running his coal-mining business.
He started his own tea party group in 2009, sold his coal-mining businesses in 2010 and, after spending his life as one of western Pennsylvania's many conservative Reagan Democrats, he switched his registration in 2011 to Republican. He won the party's nomination by spending more than $5 million of his own money to win a five-way race that included a candidate endorsed by the state party and Gov. Tom Corbett.
Associated Press reporter Kevin Begos contributed to this report.