Cardin was reelected nine times, rarely facing serious opposition. In the 2000 round of redistricting, his district was altered to add significant portions of Anne Arundel County, including the state capitol of Annapolis, to his Baltimore-based district. His last two opponents hailed from Anne Arundel and nearly carried the district's portion of that county.
In the House, Cardin was involved with fiscal issues, pension reform, and health care. His legislation to increase the amount people can store in their 401k plans and IRAs was passed in 2001. His bill to expand Medicare to include preventive benefits such as colorectal, prostate, mammogram, and osteoporosis screening was also enacted. He also authored legislation to provide a Medicare prescription drug benefit for chronic illnesses; fund graduate medical education; and guarantee coverage for emergency services. 
Cardin has also advocated, via proposed legislation, welfare reform. His bill to increase education and support services for foster care children between ages 18 and 21 was signed into law in 1999.
He authored bills to expand child support, improve the welfare-to-work program, and increase the child care tax credit. 
In 1998, Cardin was appointed Chairman of the Special Study Commission on Maryland Public Ethics Law by the Maryland General Assembly. In 1997, he co-chaired the Bipartisan Ethics Task Force in an effort to reform ethics procedures in the House of Representatives. He also held leadership positions on the Organization, Study and Review Committee and the Steering Committee of the Democratic Caucus and served as Senior Democratic Whip.
Cardin has been commended for his work with fiscal policy. He has been honored by Worth Magazine and by Treasury and Risk Management for his work protecting retirement plans and government-support medical care for the elderly. He has also received scores of 100% from the League of Conservation Voters and NAACP indicating stances that are in favor of environmental protection and civil rights. He was also one of the 133 members of Congress to vote against the Iraq Resolution. 
He was declared the winner just after 2% of the precincts reporting.Cardin won election on November 7, 2006, defeating Republican challenger Michael S. Steele 54% to 44%.
Cardin earned his B.A. degree cum laude in 1964 from University of Pittsburgh. During this time he became a member of the Pi Lambda Phi fraternity. In 1967, he graduated first in his class from the University of Maryland School of Law. Cardin also holds honorary degrees from several institutions, including the University of Baltimore School of Law (1990); University of Maryland, Baltimore (1993); Baltimore Hebrew University (1994); and Goucher College (1996).
From 1988 to 1995, he chaired the Maryland Legal Services Corp. Through much of his political career, he has continued to work with law policy.
From 1988 to 1999, Cardin served on the St. Mary's College of Maryland Board of Trustees, and in 2002, he was appointed to the St. Mary's Advisory Board for the Study of Democracy. In 1999, he was appointed to the Goucher College Board of Trustees.
On November 24, 1964, Cardin married Myrna Edelman, a teacher. They have a daughter, Deborah. Their son Michael committed suicide in 1998 at age 30.
Ben’s uncle, Maurice A. Cardin, formerly known as Morris Kardonsky, served as a Delegate representing District 5 of Baltimore City from 1951 to 1966. Maurice would play a big part in jump-starting young Ben’s political career. Meyer and Maurice were lawyers with the family law firm of Cardin & Cardin; the other partner was Jacob L. Cardin. Shoshana S. Cardin was appointed a delegate from Baltimore County District 2 to the 1967–68 Constitutional Convention, which was rejected by voters of Maryland on May 14, 1968.
In 1966, Maurice decided to not run for the District 5 seat so that his 22-year-old law student nephew Ben could run. The Cardin name proved unstoppable and Ben won, becoming a Delegate in 1967. Ben graduated from law school later that year. Ben subsequently served as Delegate representing District 42 after redistricting. Ben went on to serve as chairman of the House Ways & Means Committee at the age of 31 and as Speaker at the age of 36.
In 2002, Ben’s 32-year-old nephew, Jon S. Cardin, having similarly just graduated from University of Maryland law school in 2001, ran for election as a Delegate representing District 11 of western Baltimore County. With state legislative District 11 overlapping Congressional District 3, there were two Cardins on the ticket in this area in 2002. Present at Jon’s swearing in was the oldest living former member of the House of Delegates at 95 years of age, Meyer Cardin, Jon’s grandfather and Ben’s father. Also in attendance was Ben himself, who stated, "The next generation's taking over. After Ben announced that he would vacate his Congressional seat to run for the U.S. Senate, Jon Cardin stated that he was exploring a campaign for his uncle's Congressional seat.
| Year | Office | Election | Subject | Party | Votes | % | Opponent | Party | Votes | % | Opponent | Party | Votes | % | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1986 | Congress, MD-3 | General | Benjamin Cardin | Democratic | 100,161 | 79.11% | Ross Pierpont | Republican | 26,452 | 20.89% | ||||||||||||
| 1988 | Congress, MD-3 | General | Benjamin Cardin | Democratic | 133,779 | 72.9% | Ross Pierpont | Republican | 49,733 | 27.1% | ||||||||||||
| 1990 | Congress, MD-3 | General | Benjamin Cardin | Democratic | 82,545 | 69.73% | Harwood Nichols | Republican | 35,841 | 30.27% | ||||||||||||
| 1992 | Congress, MD-3 | General | Benjamin Cardin | Democratic | 163,354 | 99.98% | Unopposed | |||||||||||||||
| 1994 | Congress, MD-3 | General | Benjamin Cardin | Democratic | 117,269 | 70.97% | Robert Tousey | Republican | 47,966 | 29.03% | ||||||||||||
| 1996 | Congress, MD-3 | General | Benjamin Cardin | Democratic | 130,204 | 67.31% | Patrick McDonough | Republican | 63,229 | 32.69% | ||||||||||||
| 1998 | Congress, MD-3 | General | Benjamin Cardin | Democratic | 137,501 | 77.61% | Colin Harby | Republican | 39,667 | 22.39% | ||||||||||||
| 2000 | Congress, MD-3 | General | Benjamin Cardin | Democratic | 169,347 | 75.66% | Colin Harby | Republican | 53,827 | 24.05% | Joseph Pomykala, Ph.D. | Libertarian | 238 | |||||||||
| 2002 | Congress, MD-3 | General | Benjamin Cardin | Democratic | 145,589 | 65.72% | Scott Conwell | Republican | 75,721 | 34.18% | ||||||||||||
| 2004 | Congress, MD-3 | General | Benjamin Cardin | Democratic | 182,066 | 63.39% | Bob Duckworth | Republican | 97,008 | 33.77% | Patsy Allen | Green | 4,224 | 2.75% | ||||||||
| 2006 | MD Senator, Class 1 | General | Benjamin Cardin | Democratic | 965,567 | 54.20% | Michael S. Steele | Republican | 787,352 | 44.20% | Kevin Zeese | Green | 27,570 | 1.55% | ||||||||