He defeated U.S. Representative Donna Edwards in the Democratic primary and won the general election with 61% of the vote to Republican nominee Kathy Szeliga's 36%.

[12] He was also a staff member of the U.S. Senate Committee on Foreign Relations (1987–1989), and a legislative advisor for federal affairs to Maryland Governor William Donald Schaefer (1989–1991).

He led successful efforts to raise the tobacco tax, prohibit oil drilling in the Chesapeake Bay, mandate trigger locks for guns, and increase funding for education and healthcare.

Indeed, one redistricting plan after the 2000 census divided the 8th in two, giving one district to Van Hollen and forcing Morella to run against popular State Delegate Mark Kennedy Shriver.

[16] In 2002, Van Hollen entered a competitive Democratic primary against Shriver and former Clinton administration aide Ira Shapiro.

After receiving the endorsement of The Washington Post, The Baltimore Sun, and other local papers, Van Hollen defeated Shriver, 43.5% to 40.6%.

[citation needed] During the campaign, Van Hollen emphasized that even when Morella voted with the district, her partisan affiliation kept Tom DeLay and the rest of her party's more conservative leadership in power.

Van Hollen also touted his leadership in the State Senate on issues such as education funding, HMO reform, trigger locks for handguns, and protecting the Chesapeake Bay from oil drilling.

He introduced an amendment, which passed, that repealed a 9.5 percent loophole in student loans that had allowed lenders to pocket billions of taxpayer dollars.

He and Adam Schiff (D-CA) often discuss issues of National Security on the floor of the House in tandem, with particular commentary on the wars in Afghanistan and Iraq.

[21] In May 2006, Van Hollen formed a congressional caucus on the Netherlands with Dutch-born Republican U.S. Representative Pete Hoekstra from Michigan.

[23][24][25] In 2006, Van Hollen opted out of the race to succeed the retiring Senator Paul Sarbanes, saying he would rather spend time with his family and help elect more Democrats to Congress.

[28] In March 2010, when Charles Rangel was forced to resign as Chairman of the Committee on Ways and Means over ethics charges, Van Hollen played a key role in having Sander Levin succeed to the Chairmanship over Pete Stark.

However, Van Hollen and other younger members saw Stark's past intemperate comments as a liability to the Democrats in an election year.

"[32][needs update] During the 2012 Obama reelection campaign, Van Hollen participated in one-on-one debate prep with vice president Joe Biden, impersonating the Republican vice-presidential candidate Paul Ryan.

[39] Shortly after the 2016 elections, Van Hollen was selected as the Chairman of the Democratic Senatorial Campaign Committee (DSCC) for the 2018 cycle.

[41] In the immediate wake of the insurrection, Van Hollen called Trump a "political arsonist" and said "I never thought we would live to see the day that violent mobs seized control of the Capitol.

He also contrasted the police's treatment of the rioters with events that led to the use of tear gas on peaceful demonstrators, such as Black Lives Matter protests.

[44] Van Hollen also called for Trump's "immediate removal" via the Twenty-fifth Amendment to the United States Constitution and said, "we should have looked at that option much earlier.

[61] In January 2024, Van Hollen voted for a resolution, proposed by Bernie Sanders, to apply the Foreign Assistance Act's human rights provisions to U.S. aid to Israel's military.

[66] Van Hollen supports transgender rights, having signed a letter in July 2017 in opposition to an announced military ban.

[67] Van Hollen received a 0% rating for the Citizens Against Government Waste (CAGW), and the National Taxpayers Union (NTU), in 2010.

[75][76] On May 15, 2022, Van Hollen announced that he had a minor stroke over that weekend and would stay at George Washington University Hospital for a few days.