Answer by taking a quote from the following article:

Biden was born on November 20, 1942, at St. Mary's Hospital in Scranton, Pennsylvania, to Catherine Eugenia "Jean" Biden (nee Finnegan) and Joseph Robinette "Joe" Biden Sr. He was the first of four siblings in a Catholic family, with a sister, Valerie, and two brothers, James and Frank, following. His mother was of Irish descent, with roots variously attributed to County Louth or County Londonderry. His paternal grandparents, Mary Elizabeth (Robinette) and Joseph H. Biden, an oil businessman from Baltimore, Maryland, were of English, French, and Irish ancestry.

On August 27, 1966, while Biden was still a law student, he married Neilia Hunter. They overcame her parents' initial reluctance for her to wed a Roman Catholic, and the ceremony was held in a Catholic church in Skaneateles. They had three children, Joseph R. "Beau" Biden III in 1969, Robert Hunter in 1970, and Naomi Christina in 1971.  During 1968, Biden clerked for six months at a Wilmington law firm headed by prominent local Republican William Prickett and, as he later said, "thought of myself as a Republican". He disliked the conservative racial politics of incumbent Democratic Governor of Delaware Charles L. Terry and supported a more liberal Republican, Russell W. Peterson, who defeated Terry in 1968. The local Republicans tried to recruit him, but he resisted due to his distaste for Republican presidential candidate Richard Nixon, and registered as an Independent instead.  In 1969, Biden resumed practicing law in Wilmington, first as a public defender and then at a firm headed by Sid Balick, a locally active Democrat. Balick named him to the Democratic Forum, a group trying to reform and revitalize the state party, and Biden switched his registration to Democrat. He also started his own firm, Biden and Walsh. Corporate law, however, did not appeal to him and criminal law did not pay well. He supplemented his income by managing properties.  Later in 1969, Biden ran as a Democrat for the New Castle County Council on a liberal platform that included support for public housing in the suburban area. He won by a solid, two-thousand vote margin in the usually Republican district and in a bad year for Democrats in the state. Even before taking his seat, he was already talking about running for the U.S. Senate in a couple of years. He served on the County Council from 1970 to 1972 while continuing his private law practice. Among issues he addressed on the council was his opposition to large highway projects that might disrupt Wilmington neighborhoods, including those related to Interstate 95.

Did he become a democrat?