The 32-year-old was most recently with Cardiff's academy and was recommended by goalkeeper Tom Heaton who joined Burnley last week.
Kendall, who also played for the Bluebirds in a career cut short by injury, will fill the role vacated by Nigel Spink from June 1.
"He knows John Pemberton from the Sheffield United academy and comes highly-recommended by a number of people in the game, as well as our former keeper Tom Heaton, who worked with Lee at Cardiff," head coach Sean O'Driscoll told the club's official website.
"Lee reflects the type of player we want to bring to the club. He is young, enthusiastic, inquisitive and innovative.
"Lee wants to learn and develop and isn't afraid to have an opinion, which is exactly what you want from your coaching team."