The 46-year-old takes over from Harry Kewell, who was relieved of his duties a day later after just 10 weeks in charge of the League Two side.
Ardley managed to keep AFC Wimbledon in the Football League on the final day of the 2012-13 season and faces a similar battle to help County, who are 23rd in League Two, avoid relegation.
The former Wimbledon and Millwall player will be joined by his AFC Wimbledon assistant Neil Cox and is excited at the challenge ahead of him.
"There are few clubs who could have tempted me into such a quick return to management following what was obviously an emotional departure from Wimbledon, a club I love dearly," Ardley said.
"But the chance to manage Notts County is one I couldn't let pass and I will come back from my break fully refreshed and determined to drive us up the table."