Pfaff, who was an assistant coach at the University of Texas for the last seven years, had coached Canada's Donovan Bailey to the 100-metre world record in 1996.
"We are extremely excited and looking forward to working with someone as experienced as Dan," the couple said in a statement on Tuesday.
"We feel that Dan will bring an element to our training that we have never experienced before, particularly his expertise as a technician in the sprints as well as the long jump."
Pfaff had been tipped last month to be appointed after he spent time working with Montgomery at the U.S. Nationals.
The 49-year-old Pfaff is a specialist in both the sprints and field events, which would help Jones, who has said she would like to compete in both the long jump and sprints next year at the Athens Olympics.
Jones has taken this year off after giving birth to her and Montgomery's son, also named Tim, who was born on June 28.
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Bailey set the then-world record of 9.84 seconds at the Atlanta Olympics. It has since been broken by first American Maurice Greene and then compatriot Montgomery, who clocked 9.78 seconds last September in Paris.
Jones and Montgomery had been without a coach since splitting from long-term mentor Trevor Graham last year.
They worked with banned Canadian coach Charlie Francis over the northern hemisphere's winter but left him after an international uproar.
Francis was banned for life from coaching Canadian athletes after Ben Johnson tested positive for steroids following his 100 metres victory in world record time at the 1988 Seoul Olympics.