McArthur joined the GC in 2006 and became CEO in 2018, with the regulator attributing the "strengthening of protections against gambling harms" during his tenure.
However, with the UK Gambling Act review upcoming, criticism had been aimed at the GC from a multitude of directions.
While the industry felt fines from the regulator were too heavy-handed, campaigners for safer gambling have conversely argued the Gambling Commission does not do enough to protect players.
McArthur said: “I am proud of everything the Gambling Commission has achieved during my 15 years with the organisation.
"We have taken significant steps forward to make gambling fairer and safer and I know that I leave the organisation in a strong position to meet its future challenges.
"With a review of the Gambling Act underway now feels the right time to step away and allow a new Chief Executive to lead the Commission on the next stage in its journey.”
The Gambling Commission will begin the process of recruiting a CEO for an interim period.
While a long-term successor is appointed, ongoing deputy CEO Sarah Gardner and COO Sally Jones will jointly become acting CEO.
