According to Official Guinness Records,
On 1 May 2009, Nael Barghouthi, a Palestinian national sentenced to life imprisonment, became the longest serving political prisoner ever. He began his time in prison on April 4, 1978 and has now served more than thirty-two years in an Israeli jail. The previous record was held by Said Alatabah, also a Palestinian, who was incarcerated in Israel for 31 years and 26 days. He was released August 2008.
For a complete list of 2009 records, please visit 2009 Guinness Records in Israel.