Kewen was originally from Columbus, Mississippi, and the son of an Irish immigrant who served in the War of 1812.[5] At the age of thirteen, he matriculated at Wesleyan University in Middletown, Connecticut.[5] He had to return home, however, after his third year of study. Unable to complete his undergraduate education, he became an attorney by reading law in his native Columbus.[6][7] Subsequently, he relocated to St. Louis, Missouri, for the purpose of practicing law before moving to California.
Kewen died on November 26, 1879, at his home in Alhambra, California.[8] He is an honoree of the Los Angeles County Bar Association's Criminal Justice Wall of Fame (1850–2000): "In Honor of Los Angeles Judges and Lawyers Whose Outstanding Conduct and Professionalism Made Significant Contributions to the Criminal Justice System During Their Lifetimes."[9]