Miller has been an assistant under Dixon the past two seasons.
"Ryan has played a big part in our success over the past two seasons," Dixon said in a release. "He’s been a great representation of TCU and is ready to be a head coach. Ryan and his family love being at TCU and we are very fortunate to have them here."
Miller has been integral to TCU recruiting under Dixon, including the recruitment of Desmond Bane and Jaylen Fisher, the highest-rated recruit in TCU history.
Miller was an assistant at UNLV in 2015 and has coaching experience at Auburn, New Mexico, Pepperdine and Memphis.