Graduating out of Seattle Pacific University, he played for the Seattle Sounders between 1994 and 1996. Between 1997 and 1999 he turned out for the Colorado Rapids, signing with English club Fulham in 1999. Unable to become the first-choice goalkeeper at Fulham, he enjoyed loan spells with Rochdale and Reading, before signing permanently with Reading in 2002. In 2009, following 276 league appearances for the club, he transferred to Wolverhampton Wanderers.
He has won nine caps for the United States, featuring as back-up for Kasey Keller and Tim Howard in two World Cups. Following his debut for the States in 1994 he played two further games within the same month, however he had to wait almost nine years before his next international appearance, making him a player with one of the longest ever gaps between caps.
He is currently working as the head soccer coach for Newport High School in Bellevue, Washington in the United States.
Hahnemann grew up in the Seattle area in Kent and attended Kentridge High School where he was named the team's MVP his junior season. He transferred to Newport High School in Bellevue, Washington for his senior season. That year, he kept eleven clean sheets en route to being named the All-King County goalkeeper.
He played college soccer for the Seattle Pacific University Falcons. A Division II powerhouse, Hahnemann led SPU to the NCAA Division II National Championship in 1993. Over his four seasons at SPU, Hahnemann had a 64–9–5 record as a starter, with forty-six career clean sheets.
Hahnemann's professional career started when he signed with the Seattle Sounders of the A-League on May 1, 1994. In his first season with the Sounders, Hahnemann registered a .57 GAA in fourteen games to take the league's top goalkeeper honors. In 1995, he played twenty-nine games as the Sounders won the league championship. In 1996, the Sounders repeated as champions while Hahnemann kept eleven clean sheets and made 119 saves.
He waited until 1997 to join Major League Soccer (MLS), signing with the Colorado Rapids. In his first season in MLS, the Rapids went all the way to the MLS Cup before losing 2–1 to D.C. United. During his second season, he set a club record for the most games and minutes played in a single season by a goalkeeper, playing 2,520 minutes in 28 games and compiling a 16–12 record, and was named their Defender of the Year.
After two and a half seasons with the Colorado Rapids, he signed with English First Division club Fulham, for £80,000 in June 1999. He failed to displace Maik Taylor in goal though, and only made four appearances (two in the league) in total for the London club (all during their promotion season of 2000–01).
With Edwin van der Sar signed upon promotion by Fulham, Hahnemann slipped further down the pecking order and to gain playing time, he was loaned out to lower league sides Rochdale, and then, Reading during the 2001–02 campaign. He made six appearances for the latter as part of their promotion from the third tier. At the end of the 2001-02 season, Hahnemann was released by the club after spending three years. Hahnemann then signed a one-month contract extension after spending time with the club.
Hahnemann then joined Reading permanently in Summer 2002 on a free transfer, becoming their first choice 'keeper. His first full season with the Royals saw them miss out on promotion to the Premier League in the play-offs, before two successive seasons saw them narrowly fall short of further play-off finishes.
He missed just one game of the 2005–06 season that saw Reading win promotion to the top flight of English soccer for the first time in their history, as they topped the Championship with a record 106 points. He was named in that season's Championship Team of the Year by the Professional Footballers' Association.
His first season in the Premier League saw him keep thirteen clean sheets as the club finished eighth, only one place short of European qualification. He made the most saves (139) in the Premier League during 2007, but could not halt relegation in their second Premier League campaign.
He remained with the club for one further season as they attempted an immediate return to the top level, but Reading ultimately lost out to Burnley in the play-off semi finals. Subsequently Reading announced that they would not renew Hahnemann's contract making him a free agent.
On June 17, 2009, Hahnemann signed a one-year contract with newly promoted Premier League side Wolverhampton Wanderers. He was back-up to first-choice Wayne Hennessey for the opening four months, until Hennessey conceded four goals in two successive games and lost his place to Hahnemann. Hahnemann remained first choice keeper for the remainder of the season, helping the club attain survival. His form ranked him as "the Best Goalkeeper in the World" using the Castrol Performance Index system, helping earn him a one-year contract extension.
However, the 2010–11 season saw the team enter a dismal run of form that left them bottom of the league and in danger of relegation. Hahnemann was dropped after a defeat to relegation rivals Blackpool in late November and did not feature again. He was released at the end of the campaign, after the expiry of his contract.
On September 23, 2011, Hahnemann signed for Everton on a short term deal. He was released from the club on May 18, 2012 without making a first team appearance, along with Scottish international James McFadden and 4 others who also did not feature in the first team.
On September 14, 2012, Hahnemann made his long anticipated return to the Sounders. Seattle traded a conditional draft pick to Toronto F.C. for the number one allocation slot, so they would be able to sign Hahnemann.
He made his debut on October 24, 2012 against Marathón in a CONCACAF Champions League group stage match. He made his first MLS appearance for Seattle on August 3, 2013, keeping a clean sheet in a 3–0 win against FC Dallas.
On December 8, 2014, he announced his retirement from professional soccer.
Hahnemann made his international debut for the United States national team on November 19, 1994, in a 0–1 friendly defeat to Trinidad and Tobago.
After earning three caps inside a month, he did not feature for the side after the end of 1994 until playing a friendly in June 2003, shortly before the Confederations Cup, for which he was selected.
He won two further caps during 2005 and was then picked for the 2006 World Cup in Germany, and allocated shirt number 19, but was an unused substitute in all of the United States' matches behind Kasey Keller and Tim Howard as they exited at the group stage. During the group stage, he and teammate Bobby Convey became the first Reading F.C. players to be named to a World Cup roster.
On May 11, 2010, Hahnemann was named by coach Bob Bradley to the United States' 2010 World Cup squad. Hahnemann made his ninth and final appearance for the U.S. in 2011.
Marcus Hahnemann is a Republican; his wife Amanda is a Democrat. He keeps hens, and also enjoys mountain biking and hunting. Before matches he listens to heavy metal to psych himself up, and presented Five Finger Death Punch with a Wolves shirt emblazoned with a Remembrance Day poppy. He collaborated with the Reading-based band Malefice in early 2012 to release a song which will debut on Jägermeister UK's Facebook page in February 2012. Hahnemann is of German descent, his parents come from Wentorf bei Hamburg, Germany.
League ChampionshipWinner (2): 1995, 1996
Football League Championship Champions (1): 2005-06
CONCACAF Gold Cup Champions (1): 2005