Both operators, 32Red and Platinum Gaming, are owned by Kindred Group and will pay £7.1m ($8.7m) in fines.
32Red runs 32red.com and Platinum Gaming is responsible for unibet.co.uk.
An investigation by the Gambling Commission found that multiple anti-money laundering and social responsibility failures were found across the two operators.
As a result, 32Red will pay £4,195,655 in fines and Platinum Gaming will pay £2,937,599.
Kay Roberts, Executive Director of the Gambling Commission, said: “These failures highlight clearly that both operators failed to interact with customers in a way which minimises the risk of them experiencing harms associated with gambling.
“Our investigations also showed that policies and procedures were overlooked, both around customer accounts and anti-money laundering practices.
“Ultimately, it is an example which all gambling operators should take notice of to ensure they protect their customers at all times.”
32Red failed to enforce responsible gambling measures and so did not identify and protect problem gamblers.
This includes one customer who deposited £43,000 and lost £36,000 within a week.
32Red would often take the customer's word that they could afford their level of gambling without any further checks.
In regards to anti-money laundering, 32Red also failed to implement the necessary measures required by the Money Laundering, Terrorist Financing and Transfer of Funds (Information on the Payer Regulations 2017).
Henrik Tjärnström, CEO Kindred Group, said: "While we accept the outcome, and the acknowledgment that we have already taken significant steps to strengthen our processes, we also recognise that we need to work even harder to ensure a safe and compliant business.
“We appreciate the Commission's clear recognition that our operations are in an improving position and that we remain fit to hold an operating licence.
“Our commitment to reducing gambling harm across our platforms is a key part of our Journey towards Zero ambition – and we are redoubling our efforts to ensure we continue that progress."
The investigation found that Platinum Games allowed self-excluded or blocked customers to evade the ban by making a separate account.
The operator also failed to interact with customers who were struggling with problem gambling.