Mr Jaitley, who is undergoing treatment for a kidney ailment, was administered the oath of office in the chambers of Rajya Sabha Chairperson M Venkaiah Naidu.
The 65-year-old minister, elected to the Upper House of Parliament from Uttar Pradesh last month, was sworn in at a special ceremony because of his health condition.
"Took oath of office as Rajya Sabha Member representing Uttar Pradesh, April 15, 2018," Jaitley said on Twitter.
Union Ministers Ananth Kumar, Ravi Shankar Prasad, Prakash Javadekar, Piyush Goel, Hardeep S Puri, Vijay Goel and Shiv Pratap Shukla, along with leader of the Opposition Ghulam Nabi Azad, were among those present at the ceremony.
Took oath of office as Rajya Sabha Member representing Uttar Pradesh, April 15, 2018 pic.twitter.com/lpwihrRlYd- Arun Jaitley (@arunjaitley) April 15, 2018
Rajya Sabha members Bhupender Yadav, Jagdambika Pal, Conrad Sangma (now Meghalaya chief minister) and former Karnataka Chief Minister BS Yeddyurappa were also present.
Mr Jaitley had earlier been reappointed Leader of the Rajya Sabha following his election but could not be sworn in along with other members of the Upper House because of ill health.
The minister has not visited his North Block office since April 2.
He had cancelled his scheduled foreign visits and confirmed his illness in a tweet.
Mr Jaitley had undergone bariatric surgery to treat weight gain and a long-standing diabetic condition.
The surgery was first performed at Max Hospital in September 2014, but he had to be later moved to AIIMS because of complications.
He had undergone heart surgery several years ago.