According to the Sunday Times Tax List 2021, which covers tax liability for 2020, Coates and her family paid £573m ($787.6m) in taxes for 2020.
But gambling also formed two of the top three in the list, with Betfred owners Fred and Peter Done coming third.
With their 2020 wealth being documented as worth £1.2bn, the Done brothers paid £191.3m in taxed during the period.
The Bet365 owners' wealth, meanwhile, was documented as being worth £7.17bn.
In April 2020, Coates also awarded a £10m grant to the University Hospitals of North Midlands through her charity foundation.
While the COVID-19 pandemic has affected overall tax revenue in Britain, Bet365's tax numbers have gone up for gambling.
However, there was a change in the list’s methodology this year, which now counts gambling duties paid by betting businesses.
Last year, the operator's owners paid £276m in tax, which has more than doubled this year, while the Done brothers were not even in the top 10 previously.
