Born in Sutton, London, Ryan joined the Southampton Academy in 2005. He went on to captain what was a very successful Under-18 youth team and the reserve team (U23).

His professional debut on 10 October 2009 was one that Ryan will remember for all the wrong reasons, this is due to the fact in his very first game, he managed to get sent off.

Having been released by Southampton Ryan then dropped into non-league football in order to gain playing time on the pitch.

It was the 2013–14 season while playing for Mansfield that Tafazolli came to the fore, during this season he won three awards; Fans' player of the season, Chairman and Directors' player of the season, and the Stags' Association player of the season. This success courted serious interest with Mansfield having to rebuke a bid from Scottish Professional Football League side Dundee United.

On 6 June 2016, Tafazolli signed a three-year deal at League One club Peterborough United. This was during that time that Peterborough were managed by current Hull City manager Grant McCann. He was named as Peterborough's best defender and best player of the 2016–17 season.

Defending or attacking Tafazolli is a formidable opponent standing head and shoulders above his fellow squad members at six feet, five inches tall.

On 18 July 2019, Tafazolli signed a two-year deal with Hull City.