Arnold, a "Best Damn Sports Show" alum, did not file a specific date for the couple's separation, saying it was still "to be determined," E! News reported Wednesday.
The 48-year-old Arnold first sought a legal separation from the 35-year-old political consultant in August. In January, he filed a request for a judge to dismiss his petition.
Arnold and Roos met during the 2000 Democratic National Convention in Los Angeles and were married two years later.
Arnold's first marriage to actress-comedian Roseanne Barr lasted four years, from 1990 to 1994, before the couple went through a very public and bitter divorce.
A year later, Arnold married makeup artist-actress Julie Champnella. That marriage also lasted four years, from 1995 to 1999.