"My heartiest congratulations to former Prime Minister Mannmohan Singh for being honoured with Japan's second highest civilian honour, the Grand Order of the Cordon of Paulownia Flowers," Gogoi tweeted on Tuesday.
"Your achievement has made us all very proud, more so because never before such an honour has been bestowed on an Indian," he added.
Singh and his wife Gursharan Kaur is currently on a three-day visit to Tokyo where he will be given the award by Japanese Emperor Akhito.
The award is second only to Japan's highest 'Order of Chrysanthemum' and is given to statesmen and politicians who are acknowledged by Japan as having helped in the country's development or in strengthening ties with it. Singh is a Rajya Sabha MP from Assam.