Monjack married British television character Simone Bienne in Las Vegas in November 2001; they separated seven months later, and were divorced in 2006. That year, they met actress Brittany Murphy. In April 2007, they married her in a private Jewish ceremony at their Los Angeles home. The couple did not announce their engagement beforehand and seldom made public appearances together before their marriage.

In late November 2009, TMZ reported that Monjack became “incoherent” in the coursework of a flight from Puerto Rico to Los Angeles. Murphy told the responding firefighters at LAX Airport that he believed they was having an asthma assault and felt that the situation was not serious; however, EMTs disagreed and rushed him to a nearby hospital.

On December 20, 2009, Murphy died after collapsing in their bathroom. The cause was later revealed to be pneumonia, with secondary factors of iron-deficiency anemia and multiple prescription drug intoxication.