Kitsis joined the crew of Lost mid-way through the first season as a writer and producer in 2005. He was promoted to supervising producer for the second season in fall 2005. Kitsis and the writing staff won the Writers Guild of America Award for Best Dramatic Series at the February 2006 ceremony for their work on the first and second seasons. He was promoted to co-executive producer for the third season in the 2006-2007 television season. He returned as a co-executive producer and writer for the fourth season in 2008. Kitsis was nominated for the WGA Award for Best Dramatic Series at the February 2009 ceremony for his work on the fourth season of Lost. He was promoted to executive producer for the fifth season in 2009. The writing staff was nominated for the WGA award for Best Dramatic Series again at the February 2010 ceremony for their work on the fifth season. Kitsis remained an executive producer and regular writer for the sixth and final season in 2010.