Widdop told BBC Sport, "Playing for my country has given me some of the best moments and memories of my career, so this is a big decision for me.
"I will never forget the experiences of playing in the last two World Cups, in England in 2013 and especially in Australia in 2017."
The 33-year-old's career is in limbo at club level, with the off-contract Widdop unable to finish his third season at the Warrington Wolves due to a shoulder dislocation - a problem that plagued his final seasons in the NRL.
Widdop has relished his international career for both England and Great Britain, having made appearances in the halves and at fullback.
"I'd played most of my international rugby at five-eighth but Wayne Bennett switched me to fullback and I played some of the best football of my career,"
The 2012 NRL premiership winner has been involved in some absorbing contests over his representative career, such as England's last-minute loss to New Zealand in 2013's World Cup Semi-Final at Wembley and the World Cup final against Australia back in 2017.
"The semi-final against Tonga in New Zealand was incredible - I still get goosebumps thinking about it. Then to play Australia in the final at Suncorp, and come so close - they are amazing memories.
"Playing for Great Britain in 2019 also meant a lot to me - to pull on that blue and red V, which I'd watched my heroes wearing as a kid growing up.
"The fact that we moved over to Australia when I was young made playing for England and Great Britain extra special for me, and I'll always be grateful and proud for the opportunity."
England plays Samoa in the opening match of the 2022 World Cup on October 15th at St James Park, Newcastle England.