Johnson rose through the ranks at Thorp Arch, shining in reserve fixtures against contemporaries like Craig Farrell, Caleb Folan, and Tony Hackworth. Despite his promising performances and confidence in his finishing, he found it impossible to displace established strikers as Leeds battled relegation and financial turmoil in the Premier League under managers like David O’Leary and Terry Venables.

His senior opportunity finally came in April 2003 during a chaotic 6–1 win over Charlton Athletic — he replaced Alan Smith on the pitch and made his Premier League debut for Leeds, marking that as the highlight of an elusive breakthrough. He also appeared in the closing weeks against Blackburn and had a cameo role in that immortal 3–2 win at Highbury in 2003, where he celebrated Leeds’ survival as they ended Arsenal’s title hopes — Johnson came on as a substitute and boasted he 'stuck one on Dennis Bergkamp' according to his own retelling.

Over the next two seasons, Johnson made only a handful of senior appearances for Leeds — a total of just 3 league outings plus 8 as a substitute, and no goals scored in either league or cup play. With Leeds slipping into the Championship in 2004/05 and enduring financial crises, the club leaned heavily on loan movements to develop young players and balance the books.

Johnson spent much of this time out on loan, gathering match experience at Hull City, Blackpool, Sunderland, Doncaster Rovers, and Barnsley before Leeds released him in the summer of 2005. The glaring lack of playing time took a toll — Johnson later revealed he learned of his release via a newspaper headline, feeling abandoned by manager Kevin Blackwell who’d offered little encouragement to young talent despite challenging circumstances at Elland Road.

After leaving Leeds, he joined Darlington in July 2005 on a free transfer. There he finally enjoyed sustained first-team football, scoring 13 goals in 76 appearances across two seasons. While boasting versatility — often deployed wide rather than centrally — he continued to demonstrate a strong work ethic, but became unsettled by managerial changes, leading to his departure in 2007.

In August 2007 Johnson signed for Hereford United, playing a key part in their promotion from League Two in 2007/08. He scored six goals in 72 matches, including a memorable FA Cup winner against Tranmere and a late equaliser versus Wycombe that helped stabilise Hereford’s campaign.

Subsequent career chapters led him through a string of lower-league and non-league clubs, including Bury, Halesowen Town, Solihull Moors, Guiseley, a Maltese stint with Hibernians, and finishing in non-league playing roles at Hinckley United, Hinckley AFC, and even Highgate United well into his 30s. During this time he built experience coaching and managing youth, eventually founding his own academy and gaining coaching roles, including at West Bromwich Albion and later managing Highgate United in the Midland League.