It is commonly believed that Rabindranath Tagore first bestowed the name. However, this is incorrect
it was Nagar sheth of Jetpur Shri Nautamlal B. Mehta (Kamdar) Niranjan Mehta’s grand Father. who was the first to use and bestow “Mahatma” for Shri Mohandas Karamchand Gandhi on January 21, 1915 at Kamri Bai School, Jetpur, India. From then on, Gandhiji was known as Mahatma Gandhi. . Read the original documents about the day Gandhi became Mahatma (Manpatra) by clicking here! Also you will read similar Manpatra was given to Smt Kasturba Gandhi too for more info and detail please see www.kamdartree.com or http://www.nautamlalmehta.com/
National Gandhi Museum, Rajghat also has prominently displayed the documents.
Shri Niranjam Mehta, who has posted this in Facebook (https://www.facebook.com/niranjan.mehta ) has also sought views on this subject saying “It was Nautamlal Bhagavanji Mehta who first coined or used the title ‘Mahatma’ for Mohanlal Karamchand Gandhi on 21/1/1915… if any one any has other info, or claim please come up with picture, documents.and events date. “