He later spent five years at Barcelona, where he won the 1998–99 La Liga title, followed by short spells at Galatasaray, Rangers, Al-Rayyan and Al-Shamal before retiring.

He is the twin brother of Ronald de Boer, with whom he was a teammate at Ajax, Barcelona, Rangers, Al-Rayyan, Al-Shamal and the Netherlands national team.

De Boer began his career as a left back at Ajax before switching to centre-back, a position he made his own for many years in the national team.

Ajax, however, apparently backed down on that agreement after floating the club on the stock market and pledging to shareholders that it would hold both of the De Boers and build around them a team to recapture the Champions League.

[6] In January 1999, Frank and Ronald de Boer signed for Spanish La Liga club Barcelona for £22 million, joining their former Ajax manager Louis van Gaal at the Camp Nou.

[15] He is well-remembered for the arching 60-yard pass which allowed Dennis Bergkamp to score the last-minute goal that eliminated Argentina in the quarter-finals of the 1998 World Cup.

A versatile, intelligent, and elegant left-footed defender, with an ability to read the game and intercept loose balls, he was capable of playing both on the left and in the centre, and was even deployed as a sweeper.

During the 2010 World Cup, he was the assistant of the Netherlands national football team to manager Bert van Marwijk, together with retired player Phillip Cocu.

[34] In 2013, De Boer received the Rinus Michels Award for manager of the year in the Netherlands after leading Ajax to their third successive Eredivisie title.

[36] De Boer's first match in charge was Inter's final pre-season friendly, a 2–0 win against Celtic on 13 August, played on neutral ground at Thomond Park, Republic of Ireland.

[37] The club management board also approved expensive signings João Mário and Gabriel Barbosa for the team and De Boer (they were in fact linked to Mancini and Inter in July),[38] and the return to Turkey of recent acquisition Caner Erkin in the last days of transfer window.

Barbosa, however, was rarely used in Serie A matches and could not be registered in European competitions due to a penalty imposed on Inter for breaching UEFA Financial Fair Play Regulations in previous seasons.

[46] Ironically, during a press interview in the annual general meeting of the shareholders of Internazionale on 28 October, CEO Michael Bolingbroke had confirmed that the club was 100% backing De Boer.

De Boer argued that he "needed more time" in order to make a mark as manager at Inter, and thanked his fans on his Twitter profile for the support.

[50] On 26 June 2017, De Boer was announced as the new manager of Premier League side Crystal Palace, replacing Sam Allardyce.

[57] Palace winger Wilfried Zaha commented on De Boer's brief time at the club, stating "There wasn't really the right mixture [of players] for the way we wanted to play.

[61] On 23 September 2020, the KNVB announced that De Boer would be the new manager of the country's national football team, signing a contract until the end of 2022.

[65] On 5 June 2023, De Boer was appointed head coach of UAE Pro League club Al Jazira, signing a two-year contract to succeed his compatriot Marcel Keizer.