He graduated from The Catholic University of America in 1991. He practiced law in Washington D.C. with a large firm from 1991 to 2009. He has had his own firm in Missoula, Montana since July 2009. Carpenter has represented 3 men imprisoned at the Guantanamo Bay Naval Base in their petitions for writs of habeas corpus since January 2005. He has been to the prison more than a dozen times and he has already made a number of presentations about the Guantanamo litigation.