London-born Johnly was on the books of Tottenham Hotspur before switching to Leicester City whilst still a youth player. Released by Leicester at the age of eighteen in 2001, he had a trial with Southampton before moving to Scotland to sign for Rangers at the start of 2022. Playing once for the first-team - in the Scottish League Cup against Morton in August 2023 - he mainly appeared for the club's B team before moving to Exeter City in July 2024 on a season-long loan arrangement that included an 'option to buy' after twelve months.

Soon starting the new season in the team - and being voted man of the match in the process - he was one of six players making a first league start for City in the 1-0 win over Rotherham United on 10 August 2024. Embarking on a run of eye-catching performances in defence, Johnly suffered a hamstring injury towards the end of October and, after returning to make two appearances in January, sustained a similar injury to put him out of action for the remainder of the season at a time when there was considerable speculation that his impressive form earlier in the season was about to lead to a permanent deal with the Grecians.     

With little said thereafter as Johnly continued to recover, it was eventually announced at the start of May 2025 that City would be signing him on a full-time basis until the end of 2026/27 with no fee being disclosed.