Ball joined Tottenham as a trainee in July 2011, but failed to make a senior appearance for the Premier League club.
The 21-year-old spent last season on loan at Rangers, making 21 league appearances to help them win the Scottish Championship title.
"He's a young, talented defender who will give real competition for places," Millers boss Alan Stubbs said.
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Championship side Rotherham have signed Tottenham centre-back Dominic Ball on a three-year deal for an undisclosed fee.