The body, which represents digital publishing companies, already included newspaper publishers Telegraph Media Group and Guardian Media Group among its members.
However, the recruitment of The Sun and The Times-publisher News UK will boost the AOP’s ability to promote its drive to improve digital media standards in areas including ad fraud and brand safety, as set out in its Ad Quality Charter, launched last year.
Oliver Lewis, director of digital strategy and partnerships at News UK, said: "Promoting the importance of quality media and transparent, brand-safe and fraud-free advertising is a key priority for us and collaboration across the industry is vital to helping that cause.
"Quality and clarity have always been crucial for us and as a member of the [AOP] board we look forward to being actively involved with initiatives that reinforce these priorities, making it better, fairer and more sustainable for consumers, publishers and advertisers."
The charter requires member publishers to agree to use assessment and verification measures aimed at cleaning up the digital ecosystem.
AOP managing director Richard Reeves added: "Welcoming News UK to the AOP board is a natural and logical extension of our current relationship. We have similar views on multiple issues; including the need for collective industry action to increase media accountability and transparency.
"Joining forces will allow us to share learnings, resources, and influence, and establish a sustainable, digital future for the premium publishing community."