During the 2013/14 season, 15 year old Benny Ashley-Seal played a number of games for Norwich's Under-16s. He was previously at Arsenal and Tottenham before joining Norwich. He scored twice against Ipswich's Under-16s in April 2015 to help Norwich the Norwich Hospital Cup but had also played for the Under-18s whilst as a under-16.

He became a first year scholar in July 2015 and broke into the Under-21 team.

In October 2015, he was named by The Guardian as one of the top twenty prospects of his age group to look out for. Contemporaries included Liverpool’s Trent Alexander-Arnold, West Brom’s Tyler Roberts, West Ham’s Reece Oxford and Tottenham’s Marcus Edwards

On 5th May 2017, it was reported that he would be offered a professional contract with the Canaries. This though might be scuppered by reports in the Daily Mail on 23rd June 2017 that Leicester were interested in signing him. Former Norwich youth coach Dmitri Halajko is now working for Leicester.

On 19th July 2017, he played for Chelsea's development squad in a friendly against Aldershot (lost 2-1) and French side Bergerac Perigord. He then trialled with Stoke in September 2017 playing for their Under-23s in two Premier League 2 games (against Wolves and Southampton)

At the end of October 2017, Benny signed for Wolverhampton Wanderers who agreed undisclosed compensation with the Canaries for his services. He signed a two and a half year contract with Wolves. He played against his former Norwich teammates in 3-3 draw on 6th November 2017.

He made his professional debut for Wolves on 28th August 2018 in a 2–0 League Cup victory at Sheffield Wednesday, coming on as a substitute in the 80th minute for Léo Bonatini. Another League Cup appearance, against Leicester, followed as did appearances in the Football League Trophy against Scunthorpe, Mansfield and Lincoln.

He signed a new contract with Wolves on 23rd January 2019 and was then loaned out to Portuguese second division side FC Famalicao until the end of the 2018/19 season. He made five appearances, all as substitute, as Famalicao won promotion to the Portuguese top division for the first time since 1994.

After playing five games in 2019/20, he was loaned to Accrington Stanley on 31st January 2020. He made five appearances for Stanley before the Covid-19 pandemic ended the season.

On 7th September 2020 he joined Northampton Town for an undisclosed fee, signing a two year deal. "He is a big, strong and powerful striker. There is no doubt that he is a young man who can score goals." said Cobblers boss and ex-Wolves defender Keith Curle.

Northampton were relegated from League One on 1st May 2021.

On 20th May 2022 it was reported that Benny would leave Northampton at the end of the season. He had made only six appearances in 2021/22, scoring twice. This brought his Cobblers' total to 35 games and 5 goals.

At the end of July 2022 he signed for Finnish side KTP. He made seven appearances for KTP.

On 18th March 2023 he joined Scottish side Hamilton Academical until the end of the 2022/23 season. He left on conclusion of the season, having played eight games and scoring once.