Guo is also the chief of China's banking and insurance regulator
His appointment was rumoured earlier when the NYT reported it overnight, but it's official now.
Previous PBOC governor Zhou held both the governor role and the party chief role to the PBOC, but now Guo is taking over the latter's role while earlier appointed Yi Gang will take over as governor.
In essence, you can think of it as Yi would not be able to move or do anything without Guo knowing or getting Guo's approval - or for that matter vice premier Liu He's approval.
It's not going to change much of how the central bank is run, but it solidifies the notion that president Xi Jinping is not willing to take any chances as he seeks to lay out his plans in cleaning up the country's financial system.
Update: PBOC is also said to have appointed Guo as deputy governor as well.
