Routis signed an initial one-year deal with the Bantams last summer after impressing on trial during pre-season. The club inserted the option for another year into Routis' original contract, which City have now activated.
The 25 year-old made 23 appearances in total for City last season during his first campaign in English football.
The former Servette player featured at right back, centre half and in central midfield for City, making himself a handy member of Phil Parkinson's squad in the process.
Parkinson said: "We have been pleased with Christopher's progress during the year and we look forward to working with him again next season."
Routis himself added: "I have learned so much this season.
"English football is different to what I was used to before but I am really happy because this is a big time in my career.
"Everybody told me that the first season in England would be difficult as a French player but I have done that now and I am excited to start my second."