Ram Nath Kovind is the first Bharatiya Janata Party leader and second Dalit in Rashtrapati Bhavan.
Ram Nath Kovind was administered the oath of office to 'preserve, protect and defend the Constitution and law' by Chief Justice of India J S Kehar in an impressive ceremony in the Central Hall of Parliament.
The 71-year-old laweyer took the oath in Hindi to thunderous applause and thumping of desks by the gathering, which included outgoing President Pranab Mukherjee, Vice-President Hamid Ansari, Prime Minister Narendra Modi, Lok Sabha Speaker Sumitra Mahajan and former President Pratibha Patil.
Once President Kovind had been sworn in, Mukherjee and he exchanged seats on the dais after which he delivered his maiden speech as President.
"I am accepting this position with all humility and I am grateful for this responsibility. I feel privileged to walk on the same path as Dr Rajendra Prasad, Dr Sarvapalli Radhakrishnan, Dr A P J Abdul Kalam and Pranabda," Kovind said.
"My journey from a small village to the President's House has been long but interesting. A nation grows only when development for all is ensured. Hum sab ek hain aur ek hi rahenge (We are one and we will always be one)," the President said to applause.
Former prime ministers H D Devegowda and Dr Manmohan Singh, United Progressive Alliance Chairperson Sonia Gandhi, former Lok Sabha speaker Meira Kumar, former deputy prime minister L K Advani, Union ministers and foreign diplomats were also present.
President Kovind was given a 21 gun salute to mark the assumption of office of the highest Constitutional post in the land.
The elaborate ceremony for the change of guard at Rashtrapati Bhavan commenced with a gentle knock on the door of President-elect Ram Nath Kovind's Akbar Road home.
It was Major General Anil Khosla, military secretary to the President, inviting Kovind and his wife Savita to Rashtrapati Bhavan where President Pranab Mukherjee was waiting for them in the study.
The President and the President-elect then walked to the grand forecourt of Rashtrapati Bhavan where they were escorted to the saluting dais.
President Mukherjee took the last salute of the President's Bodyguard with President-elect Kovind standing to his left.
Mukherjee and his successor drove down Raisina Hill to the Central Hall of Parliament in a black limousine.
Escorting them was a grand equestrian procession by the President's Bodyguard, dressed in white ceremonial uniforms and blue turbans with gold ornamental work.
The road from Rashtrapati Bhavan to Parliament was lined with 1,000 jawans from all three services of the armed forces offering the traditional 'hazaar salaam' to the President, who is the supreme commander of the defence services.
The procession reached gate five at Parliament where Vice-President Hamid Ansari, Lok Sabha Speaker Sumitra Mahajan and Chief Justice of India J S Kehar received President Mukherjee and President-elect Kovind who were then taken to the Central Hall.
After he took the oath of office, President Kovind and former President Mukherjee left for Rashtrapati Bhavan in the presidential limousine.
The skies opened up as the procession made its way from Parliament to Rashtrapati Bhavan. The black tarmac of Rajpath seemed washed clean as the President's Bodyguard marched with military precision in the pouring rain.
After President Kovind and Mukherjee arrived at Rashtrapati Bhavan, the former took charge after signing the register.
After the event, Mukherjee proceeded to his new residence, 10, Rajaji Marg.
Earlier in the day, Kovind and his wife Savita paid tribute to Mahatma Gandhi at Rajghat.
Kovind was born in Kanpur, Uttar Pradesh.
A commerce graduate, he studied law at Kanpur University, practised law in the Delhi high court and Supreme Court.
He was the central government's standing counsel in the Supreme Court from 1980 to 1993.
Kovind, who headed the Dalit Morcha from 1998 to 2002, also led the All-India Koli Samaj.
Elected to the Rajya Sabha in April 1994 from Uttar Pradesh, he served two consecutive terms in the Upper House of Parliament till March 2006.
'Congratulations to Shri Ram Nath Kovindji on taking oath as the President of India,' Prime Minister Modi tweeted.
'Very inspiring address by President Kovind, which beautifully summed up the essence of India's strengths, democracy & diversity,' Modi later tweeted.
Additional inputs: ANI