The 40-year-old edged out Michael Appleton in a rigorous selection process which only saw the decision made an hour before his unveiling on Monday afternoon.
"We have had a very arduous process to find our new manager," Ryan said. "We have gone through this process which has been finalised on Monday and we have unanimously decided on a young, aggressive person who manages like he played.
"We knew it was a critical appointment having just got back into the Championship. We wanted someone who could take us on from where we are now and we were very impressed with Paul with the way he played against us for Oldham three times last season.
"We feel he has all the credentials to become a fantastic manager in years to come.
"He is very organised, very hard working, very enthusiastic and although there was some very stiff competition he came out top, in a 14-point criteria and also in the interviews. We have done all we can to acquire the best manager we can for Doncaster.
"There was intense competition and Doncaster Rovers is now a coveted job whereas 20 years it maybe wasn't."