The Maine Coon from Reno, Nevada, was identified by Guinness World Record officials as measuring 123.2cm from nose to tailbone.
Stewie's owners, Robin Hendrickson and Erik Brandsness, say they determined to try for the record after hearing countless people say they were amazed by Stewie's length.
Ms Hendrickson said maine coon are recognized as the "gentle giants" of the cat world.
The record was formerly held by another Maine Coon that measured 121.9cm.
