Emmanuel Dennis was born on 15 November 1997 in Nigeria. He played as a forward, primarily on the left wing. Dennis' physique was well-suited for such a role; he was 5ft 8in (1.75m) tall and weighed 10st 7lb (67kg).
In March 2016, he transferred from Abuja in the National League in Nigeria to Zorya Luhansk in the Premier League in Ukraine. His debut season, 2016-2017, saw him making 22 first team appearances and scoring six goals in league matches.
Following his stint in Ukraine, Dennis transferred to Club Brugge in the Pro League in Belgium in July 2017 for a fee of around £1.1m. He was a notable presence for Club Brugge from 2017 to 2020, making a total of 60 appearances and contributing 17 goals across three seasons. However, he saw reduced play in the 2020-2021 season, during which he made only nine league appearances.
January 2021 saw Dennis moving to Cologne in the Bundesliga in Germany on loan, where he also made nine league appearances. This was followed by a transfer to Watford in the Championship in England in July 2021 for an undisclosed fee. He made considerable contributions while at Watford, making a total of 52 appearances and netting 14 goals over three seasons.
August 2022 heralded a substantial change in his career as Dennis transferred from Watford to Nottingham Forest in the Premier League for around £20m. He made 19 appearances and scored two goals during his season there. However, his time at Nottingham Forest was interrupted by several loan moves.
Dennis was loaned out to Istanbul Basaksehir in Turkey's Süper Lig in September 2023, where he made eight appearances. In January 2024, he was loaned back to Watford, who had since dropped to the Championship.
This return to Watford reflected similar performance statistics to his prior engagement with the club. Yet, upon completion of his loan, he returned shortly to Nottingham Forest before promptly being loaned out to Blackburn Rovers in the Championship in February 2025, making six appearances in that season.
After his loan at Blackburn Rovers ended in June 2025, Dennis returned once more to Nottingham Forest. His future career trajectory from there remains yet to be seen.