Rotherham sacked Andy Scott last month after seeing their League Two promotion hopes fade, and have pulled off a significant coup in landing Evans from ambitious Crawley who sit fourth in the table, two points off the automatic promotion places.
Chairman Tony Stewart said: "The board and myself were extremely impressed with what Steve had to say, which matched our vision and ambition for Rotherham United.
"We have taken our time, looked at a high number of high-calibre applications but Steve stood out and we are delighted he has agreed to take the job."
Evans, who led Crawley to promotion from the Blue Square Bet Premier last season and leaves them fourth in League Two, managed Boston between 1998 and 2007 but landed a 20-month suspension and a conviction for tax fraud during his tenure there.
A Crawley statement said: "The club would like to place on record its appreciation of Steve's efforts since he came to the club in May 2007 and in particular taking Crawley Town into the Football League for the first time in our history.
"First-team coach Craig Brewster has been appointed caretaker manager until the end of the season, when the position will be reviewed, and the club would urge all of our supporters to get behind Craig and the squad as we push for promotion to League One."
Assistant manager Paul Raynor has also left the club with immediate effect.