Senator John McCain took the political world by surprise on Friday when he named Sarah Palin, a little-known governor of Alaska, as his running mate on the Republican presidential ticket.

Ms. Palin, 44, is a social conservative, former union member and mother of five who has been governor for two years. She hardly featured in any of the much discussed McCain campaign short lists for vice president but she definitely is enormously popular in her state.

“She’s not from these parts, and she’s not from Washington, but when you get to know her, you’re going to be as impressed as I am,” announced McCain to 15,000 people gathered in a basketball arena in Dayton, Ohio, shortly before Palin stepped onto the stage with McCain surrounded by her husband and four of their five children, to become first woman to grace a Republican ticket.

It took only a few moments for Palin to make an impact the disappointed supporters of Senator Hillary Rodham Clinton as she went on to praise not only Mrs. Clinton but also the only other woman in American history who has been on a presidential ticket, Geraldine A. Ferraro, Walter F. Mondale’s Democratic running mate in 1984.

“Hillary left 18 million cracks in the highest, hardest glass ceiling in America, but it turns out the women of America aren’t finished yet, and we can shatter that glass ceiling once and for all,” Ms. Palin said to huge ovation.