The declaration of this day came after the call for the adoption of 21 June as International Day of Yoga by Indian Prime Minister Narendra Modi during his address to UN General Assembly on September 27, 2014 wherein he stated:
"Yoga is an invaluable gift of India's ancient tradition. It embodies unity of mind and body; thought and action; restraint and fulfilment; harmony between man and nature; a holistic approach to health and well-being. It is not about exercise but to discover the sense of oneness within yourself, the world and the nature. By changing our lifestyle and creating consciousness, it can help us deal with climate change. Let us work towards adopting an International Yoga Day."
 In suggesting June 21, which is the Summer Solstice, as the International Day of Yoga, Narendra Modi had said that the date is the longest day of the year in the Northern Hemisphere and has special significance in many parts of the world.
From the perspective of yoga, the Summer Solstice marks the transition to Dakshinayana. The first full moon after Summer Solstice is known as Guru Poornima. According to Sadhguru Jaggi Vasudev, in the yogic lore, the first transmission of yoga by Shiva, the first Guru, is said to have begun on this day. Dakshinayana is also considered a time when there is natural support for those pursuing spiritual practices. Govind Gurbani Yog Guru / Vice President of Rajasthan Swasthya Yog Parisad Jaipur India informed that on 21 June fifty thousand followers of Yoga will perform Yoga in Rajasthan.
This initiative found support from many global leaders. At first, the Prime Minister of Nepal Sushil Koirala supported the proposal of Modi. More than 177 countries including USA, Canada, China and Egypt have supported this move, including 175 nations co-sponsoring the resolution. It had the "highest number of co-sponsors ever for any UNGA Resolution of such nature." On Dec 11, 2014, the 193-member U.N. General Assembly approved by consensus a resolution establishing June 21 as 'International Day of Yoga'. The resolution also saw a record number of 177 countries co-sponsoring it.
Prior to the 2014 UN resolution declaring June 21 as International Day of Yoga, formal and informal groups of yoga teachers and enthusiasts celebrated World Yoga Day on dates other than 21 June in support of various causes. In December 2011, international humanitarian and meditation and yoga Guru Sri Sri Ravi Shankarand other yoga gurus, supported the cause from the delegation of the Yoga Portuguese Confederation and together gave a call to the UN to declare June 21 as World Yoga Day.
The two-day conference titled ‘Yoga: A Science for World Peace’ was organized by The Art of Living and SVYASA Yoga University, Bengaluru, jointly with Yoga Portuguese Confederation of Lisbon, Portugal on 4th and 5 December 2011, at The Art of living International Centre. On that day, under the leadership of Sri Sri Ravi Shankar a proclamation was signed for having UN and UNESCO declare the 21 June as ‘World Yoga Day’ at Art of Living international Centre at Bangalore, India. HH Sri Sri Ravi Shankar, Founder, The Art of Living; HH Shri Swami Bala Gangadharanath of Adi Chun Chun Giri Mutt; HH Swami Paramátmánanda, General Secretary of the Hindu Dharma Acharya Sabha; BKS Iyengar, Ramamani Iyengar Memorial Yoga Institute, Pune; HH Swami Ramdev, Patañjali Yogpeeth, Haridvar; HH Dr. Nagendra, Vivekánanda Yoga University, Bengaluru; HH Jagat Guru Amrta Súryánanda Mahá Ráj, President of Yoga Portuguese Confederation; HH Subodh Tiwari, Keivalyadhama Yoga Institute; Dr. D.R Kaarthikeyan, Advisor: Law-Human Responsibilities-Corporate Affairs and Dr. Ramesh Bijlani, Aurobindo Ashram, New Delhi were present for the conference. Emphasizing on the importance of yoga, Sri Sri Ravi Shankar said, “Yoga makes you like a child again. When there is yoga and vedanta, there is no lack, impurity, ignorance and injustice. We need to take yoga to the doorstep of everyone and free the world of misery.” According to Jagat Guru Amrta Suryananda, "The idea to celebrate World Yoga Day originated 10 years ago. But this was the first time yoga gurus from India were endorsing it in large numbers, said Jagat Guru Amrta Suryananda Maha Raja, president of the yoga portuguese confederation.," even before the collective call for such a day by Indian Yoga Gurus in 2011. Following the adoption of the UN Resolution, Sri Sri Ravi Shankar lauded the efforts of Narendra Modi, stating that "It is very difficult for any philosophy, religion or culture to survive without state patronage. Yoga has existed so far almost like an orphan. Now, official recognition by the UN would further spread the benefit of yoga to the entire world."