In those games, Richardson steered the side to five wins and three draws.
He said: "I'm delighted to have landed the job full-time.
"The effort and desire to improve has been fantastic from everyone at the club, and hopefully we can build on what we have already achieved.
"I would like to thank the lads for their efforts so far, and all the coaching staff too. We will now be aiming to keep our run going."
Richardson has made nearly 300 appearances for the club, after joining as a player in March 1996.