He was released at apprentice level. However, when the apprenticeship scheme was revamped he was re-signed as a trainee at Grimsby Town and after 13 appearances in the Second Division he signed professional terms. At the start of McDermott's career he was a utility player but then established himself as a regular right-back for the Mariners.

He won Grimsby Town's 'Player of the Year' award a record three times.^{[citation needed]} In 1994, McDermott suffered an injury and was injured for nine months. He regained his place in the team in 1996 and was linked with moves to Sunderland and Ipswich Town,^{[citation needed]} but he did not leave Grimsby Town. A quote from him in 2005 on the situation of present-day footballers is:

"If someone would rather sit in the reserves at a big club and drive around in a Ferrari rather than going out on-loan and playing, then I think it's a sad day."^[2]

There was a time where he was expected to move to fierce rivals Hull, but the deal never materialised.

He was appointed captain by player/manager Paul Groves, and won BBC Radio Humberside 'Sports personality of the year' award. Other highlights in his career included the win over Tottenham Hotspur in the League Cup. Further highlights followed in the 2005–06 season as he had his second testimonial against local rivals Hull City and was included in Four Four Two magazine's list of the top 50 players outside the Premier League.^{[citation needed]}

Throughout his 20-year career, McDermott has experienced promotion or relegation nine times. He considers his Man of The Match award in the Football League Trophy victory in 1998 to be the highlight of his career.^{[citation needed]}

McDermott was described by one Grimsby Town fanzine as a defender who 'defends without tackling'; meant as a compliment to his ability to shackle opposition strikers without committing fouls.^{[citation needed]}

McDermott announced on 20 December 2006 that he would retire at the end of the 2006–07 season.^[3] McDermott played his final home game for Grimsby on 29 April 2007 against local rivals Lincoln City. The game finished 0–0. McDermott made his final appearance for Grimsby away to Shrewsbury, the final league game of the season, and coincidentally Shrewsbury's final league game at Gay Meadow. McDermott was substituted in the 73rd minute as Grimsby fought out a 2–2 draw. Upon leaving the field, play paused briefly as both sets of fans applauded McDermott off the field.

McDermott's autobiography It's Not All Black & White, went on sale in August 2013. Co-written by Simon Ashberry, the book is published by The History Press. He took part in two events to mark the launch of the book - An Evening With John McDermott hosted by the Mariners Trust at Grimsby Town and a book signing sessions at Waterstones in Grimsby.

In July 2007, McDermott applied for the vacant manager's job at Boston United but was overlooked for the position, and United in turn appointed Tommy Taylor. In October 2008, McDermott distanced himself from speculation linking him to managing Grimsby Town after the sacking of Alan Buckley. McDermott then turned to coaching the Grimsby Institute Academy male and female football teams.

In October 2009, he was once again linked with the vacant managers post at Grimsby following the sacking of Mike Newell.^{[citation needed]} This time McDermott as well as Dean Windass expressed a desire to take the job. McDermott was appointed assistant manager of Harrogate Town ahead of the 2010–11 season. In 2017, McDermott became the Director of Football at Cleethorpes Town, taking them to Wembley in the FA Vase Cup Final, before being named as Alfreton Town manager in May 2017.

In May 2019, McDermott was appointed Assistant Manager of Boston United.^[4]

McDermott has also worked as an academy coach for Scunthorpe United and has worked as a coach for Grimsby College.^[5]

On 16 September 2022, McDermott was reunited with former Boston manager Craig Elliot by joining him as assistant manager at Matlock Town.^[6] On 11 December 2022, Elliott and McDermott resigned from Matlock to take up similar positions at Buxton.^[7]

^[8]

Grimsby Town edit

• Division Four runners up, Promoted: 1990
• Division Three 3rd place, Promoted: 1991
• Football League Trophy winner: 1998
• Second Division playoff winner: 1998
• Football League Two Play-off runner up: 2005–06
• Supporters Player of the Year: 2005
• Supporters Young Player of the Year: 1987, 1990, 1992
• Grimsby Town F.C. Special Achievement Award: 2007

• John McDermott at Soccerbase  
• Player profile at Cod Almighty fanzine