It is unclear why the triple premiership-winning coach has made the call, though a report on Melbourne radio station SEN on Monday night suggested "general burnout" is a factor.
Hardwick, who was contracted to Richmond until the end of 2024, is expected to address the issue at a press conference on Tuesday.
The 50-year-old led the Tigers to premierships in 2017, 2019 and 2020.
But with Richmond having won just three of 10 matches this season, critics have called an end to their golden era.
It is unclear whether Hardwick, a veteran of 307 games at the helm, will leave his post immediately or coach Richmond against Port Adelaide on Sunday.
The Essendon and Power premiership defender took over as coach of Richmond in 2010 and won just six games in his first season at the helm.
He endured three consecutive elimination final defeats bwtween 2013-2015 and missed the finals in 2016.
There was huge pressure on the club and Hardwick at the end of that season but Richmond resisted the urge to make a change and the decision paid dividends.
The Tigers ended a 37-year premiership drought in 2017 and won three flags in four years.
They have played just one final since then; an elimination defeat to Brisbane last year.
Hardwick's career coaching record stands at 170-6-131.
He is Richmond's longest-serving coach and sits 22nd for the most AFL/VFL games coached in competition history.
Hardwick's decision will have a flow-on effect in the coaching landscape.
Port Adelaide's Ken Hinkley is out of contract at the end of this season and West Coast's Adam Simpson is under huge pressure after a horror run.
There is also doubt over Alastair Clarkson, who is on indefinite leave from North Melbourne.
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