Clini was the director of the department of environmental protection and industrial medicine in Venice-Porto Marghera in the 1980s. He became the director general of the Italian environment ministry in the 1990s. He chaired the Italian expert-level delegation at the Rio conference on environment and development in 1992, and the Kyoto conference on climate change in 1997. From 2000 to 2001 he served as co-chairman of the G8 task force on renewable energy. He was also co-chairman of the European environmental and health committee of the United Nations economic commission for Europe. In 2006, Clini was named as chairman of the global bioenergy partnership. He also served as the director general of the Italian ministry of environment, land and sea. On 16 November 2011, Clini was appointed minister of environment, land and the sea. His tenure ended in April 2013 and Andrea Orlando replaced him in the post.