According to Official Guinness Records,
The longest applause lasted for 2 hr 00 min 32 sec during a performance by Dustin Luke Nelson (USA) at the Walker Art Center's Open Field in Minneapolis, Minnesota, USA, on 26 June 2014. Dustin's performance was a conceptual performance which aimed to bring the community together and appreciate the act of applause itself.
For a complete list of 2014 records, please visit 2014 Guinness Records in United States.