Efan began his career with non-league Sutton who sold him to Bournemouth in April 1990. A tally of 25 goals in 74 games convinced Norwich boss Mike Walker to pay £500,000 for him in March 1993 in an attempt to boost Norwich's faltering Premiership Championship bid. Although this was unsuccessful (they finished third), this was not Efan's fault as he scored twice. The next season was as memorable as he scored Norwich's first European goal against Vitesse Arnhem in the UEFA Cup and put four past Neville Southall in the Everton goal at Goodison Park. His fourteen goal tally for the 1993-94 season would be higher was it not for his call-up to the Nigerian international squad for the African Nations Cup. He missed six games whilst playing only 60 minutes for the Nigerians against Zaire. He was also included in Nigeria's World Cup USA 94 squad but did not make an appearance. Efan left Norwich the following season in a £1 million transfer to Wimbledon where his pace has been his greatest advantage.

In early September 1998, Efan submitted a transfer request stating that "I must get away from Wimbledon. I have handed in a written transfer request and my aim is to join a bigger Premiership club" (Daily Mirror). Nottingham Forest were favourites to sign Ekoku but failed to do so as they had difficulties parting with Pierre van Hooijdonk first. Martin O'Neill was also interested in signing £4million rated Efan for his Leicester City whilst Everton were also linked. Southampton made an offer in the end of October 1998 but were quoted a figure of £4million which would be double their record signing.

At the end of 1999, Efan agreed to come off the transfer list and discuss a new contract with Wimbledon. He also regained his place in the Wimbledon line-up as well as training with the Nigerian side. However his position with the Dons was threatened by their new £7.5million signing John Hartson. The Daily Mirror and The Daily Mail suggested on January 22nd 1999 that Southampton manager Dave Jones would again attempt to sign Efan for the Saints. At the end of the 1998/99 season, Efan was placed on the transfer list by Wimbledon, possibly to be replaced by Ade Akinbiyi. The Sunday Mirror suggested otherwise on 30th May proposing a swap between Wimbledon and Derby with Efan heading to Pride Park and Dean Sturridge making the move south. The accuracy of this story could be questioned when it claims both players are rated at £5million !

As the new season began it became apparent that Efan didn't fit into the plans of new Dons boss Egil Olsen. On 25th August 1999 Efan signed for Swiss side Grasshoppers of Zurich who were then managed by former Blackburn boss Roy Hodgson. The transfer resulted from Efan's appearance for a Nelson Mandela XI in a clash against a World XI managed by Hodgson who had tried to sign Efan whilst at Ewood Park. Efan signed a three year contract with Grasshoppers and his lawyer Gary Blumberg said "This is an exciting opportunity for Efan and I believe its a unique deal given that a Premiership player is joining a Swiss club. Having played for the Mandela XI it was a good chance for Efan to put himself in the shop window because he didn't seem to be getting any help at Wimbledon. Roy Hodgson watched Efan and after that he was soon in touch and wanting to put together a deal. Efan sees this as a step up because Grasshopper are a bigger club than Wimbledon and the move also gives him the chance of European football" (taken from Yahoo's Teamtalk Service).

However the News of the World reported on 20th August 2000 that Efan was hoping to return to England following the sacking of Hodgson. In October 2000, Sheffield Wednesday boss Paul Jewell brought Ekoku back to England on a three month loan deal although the deal nearly collapsed over personal terms. This was extended to the end of the season even though The News of the World speculated that Crystal Palace would attempt to bring Efan back to Selhurst Park on a permanent move (17th December 2000). Although Efan returned to Switzerland in May 2001 at the end of the 2000/01 season., a permanent move to Sheffield was completed on the 31st July 2001.

In March 2002, Efan was surprisingly linked with moves to Division Two outfits Brentford and Wycombe. Apparently they knew something that wasn't in the public domain as Efan was placed on the transfer listby Wednesday on April 30th 2002 by new manager Terry Yorath. At the end of May 2002, he was linked with a move to Gillingham to replace prison-bound striker Marlon King. Efan's association with Hillsborough came to an end in September 2002 when both parties agreed to a termination of his contract. He quickly sought a new club and by the end of September 2002, he was training with Luton. He trained with Rushden & Diamonds in mid October but they decided not to pursue their interest in him any further.

On March 27th 2003 (Transfer Deadline Day), Efan returned to London and signed for Brentford. However he was released two months later.

Although primarily working as a commentator for the BBC, Efan followed Carlton Palmer's example and signed a short-term contract with Irish side Dublin City at the end of August 2004.

In October 2006, Ekoku was training with the Middlesbrough F.C. squad. Though he has yet to sign any official contract. It is widely tipped that he will be joining the coaching staff possibly as a player/coach, as he has obtained all of his FA and UEFA Cocahing Badges

At the end of February 2012, Efan was voted into Norwich City's Hall of Fame