Olsen is best known for his long-term association with D.C. United of Major League Soccer (MLS), first as a player then as a coach.

Born in Middletown, Pennsylvania, Olsen grew up playing for FC Delco, an elite club program near Philadelphia.

[7] He played his youth soccer for premier team FC Delco, where he was inducted into the club's Hall of Fame.

[9] Olsen entered the league as a Project-40 player, and was allocated to D.C. United on December 27, 1997, shortly after finishing his junior season at UVA.

After he recovered from the ankle injury in late 2000, Olsen was loaned by United to Nottingham Forest of the English First Division, where he immediately impressed and soon became a fan favorite.

Although his speed was limited due to his injuries and surgeries, Olsen was able to adapt to a new position as a center midfielder.

He served as Captain when Jaime Moreno was away on national team duty, scored his first career hat trick in a 4–2 win over New York Red Bulls on June 10, and enjoyed his best season in MLS.

[15] Despite said problems, Ben Olsen was able to make one MLS appearance against the Los Angeles Galaxy on June 28, 2008.

The crowd greeted him with the loudest ovation of the day and a tifo that read "Ben Olsen" and "Heart Of A Lion".

[16] After playing just 15 minutes Olsen responded to the media by stating, "It wasn't great; I was like a wounded animal out there."

Only three days earlier Olsen stated in an online chat hosted by The Washington Post that he was committed to playing another year.

In his honor the Wizards announced $14 tickets to a game against the Philadelphia 76ers, which reflected Olsen's jersey number for United.

[24] After moving to a controlling midfield position, Olsen was one of the selections on Bruce Arena's 2006 FIFA World Cup roster, having scored goals in the U.S. team's early 2006 win over Guatemala and in an April tie with Jamaica.

Olsen made his lone World Cup appearance against Ghana in a 2–1 loss, replacing an injured Claudio Reyna.

Although United officials interviewed at least seven candidates, including Hertha Berlin manager Lucien Favre, the club appointed Olsen to the head coaching position.

This occurred despite the fact that United President and CEO Kevin Payne had continuously ruled him out during the months leading up to the decision.

[28] In a largely disappointing 2013 season where United was last in the Eastern Division, Olsen led the team to the 2013 Lamar Hunt U.S. Open Cup Final against Real Salt Lake.

In 2019, Olsen became the youngest head coach in MLS to reach 100 wins as a manager, achieving the title at 41 years old.

[33] The couple later featured in a popular TV commercial for Dick's Sporting Goods, in which Olsen enjoys an impromptu soccer skills exhibition with fellow MLS players Brian Ching, Duilio Davino and Christian Gómez, before he and Megan chase their screen son, "Dawson", out of the store when he has the temerity to ask for a David Beckham jersey.

[34] Olsen has rented out the apartment below his Northwest, Washington, D.C. town house to numerous teammates, including to D.C. United goalkeeper Zach Wells during the 2008 season.