[2] Descalzi started to work at Eni in 1981,[3] when he joined the multinational company operating in the production and distribution of energy as a reservoir engineer, then he became Project Manager for the activities in North Sea, Libya, Nigeria and Congo.

In 1990, Descalzi was appointed Head of Reservoir and operating activities for Eni Italy, a position which led him to develop a new model and to increase production to 250,000 barrels per day.

[4] In 1998 he became Vice President and Managing Director of NAOC: during this period He started the export of gas produced at the NLNG liquefaction plant and the development of deep-water offshore local projects.

[22] On April 12, 2023, Descalzi was confirmed by the Meloni government as head of Eni for the fourth consecutive term, a record in the history of the six-legged dog company.

[23] Descalzi and other Eni executive leadership have faced legal charges for corruption involving $1.1 billion,[27][28] based on the company's operations in Nigeria[29][30][31] and the Republic of the Congo.

[35] On October 8, 2024, the Court of Brescia sentenced prosecutors Fabio De Pasquale and Sergio Spadaro to 8 months in prison in the Eni-Nigeria trial, on the grounds that they had omitted evidence favorable to the defendants, including Claudio Descalzi.