John O'Brien (born in August 29, 1977 in Los Angeles, California) is a soccer player, one of the first Americans to earn a starting spot with a notable European team, which he did with Ajax Amsterdam. He currently plays for ADO Den Haag.

O'Brien had his first trial with Ajax at the age of 14 and signed an amateur contract with the Dutch giants in 1996 as a 17-year old. After two years on their youth teams, Ajax offered O'Brien a professional contract in 1998. He spent the 1998-99 season on loan to FC Utrecht and made his Ajax debut in 1999. Since then, he has been a regular for a team, usually playing at left back, winning Eredivisie in 2002 and 2004. Unfortunately, chronic injuries have limited O'Brien's playing time in recent years. He left Ajaz for ADO in February 2005.

With the US national team, O'Brien earned his first cap against Austria on April 22, 1998, but was left off the US squad for the 1998 World Cup. He played in the 2000 Summer Olympics, helping to lead the US to a fourth-place finish. O'Brien became a regular with the senior team under Bruce Arena, and came into his own at the 2002 World Cup. Playing in defensive midfield, he scored the opener in the shock 3-2 win over Portugal and played every minute of every game for the United States.