Now that her husband is part of the ticket, her newly appointed aides say, she is ready to do whatever the campaign asks of her. She arrives here on Monday and will plunge into an array of activities.

Dr. Biden grew up in Willow Grove, Pa., a Philadelphia suburb, the oldest of four daughters. Their father was a bank teller who became president of a savings and loan; their mother stayed home to raise them.

She started working at 15, telling an interviewer last year, “I wanted my own money, my own identity, my own career.”

When Mr. Biden first called her that night in 1975, she told him that she had voted for him in 1972. She also knew the tragic story of his wife, Neilia, who was killed with their baby daughter in 1972 when a truck broadsided their car as they were Christmas shopping. Their two sons, Beau and Hunter, were injured but recovered.

“Funny thing was, by the time Joe called, she’d almost resolved to quit dating,” Richard Ben Cramer wrote in his political biography, “What It Takes,” in which he delved into the lives of the candidates running for president in 1988. “She’d married young, it didn’t last, and after that, when she went back to college, well ... she was a senior, but 24 years old.”

Mr. Cramer said she was impressed that Mr. Biden had showed up in a suit and shook her hand good night. She called her mother that night to say she had finally met a gentleman.

Their lives quickly became intertwined, and eventually, his young sons asked him when “we” were going to get married. He had to ask her five times before she overcame her hesitation at becoming a full-time mother and meeting the public demands of a political spouse. Of Mr. Biden, she said that she came to realize that “anybody who can love that deeply once can do it again.”