Dionne was born in Gossas on 22 September 1959.[3] When his mother gave birth to him, she took refuge in a locality where her grandmother lived. His father worked as a police commissioner.[4]
Dionne worked as a computer engineer specializing in applied economics, and worked in a West African bank and as head of the Economic Office at the Senegalese Embassy in France.[5] He was Director of the Cabinet of Prime Minister Macky Sall from 2005 to 2007, and when Sall moved to the post of President of the National Assembly in 2007–2008, Dionne continued working under Sall in the same capacity.[6] In March 2014, he was appointed to coordinate the Plan Sénégal Emergent (PSE), an economic and social development plan to make the country an emerging economy by 2035. He became the Prime Minister in July 2014. During his tenure as Prime Minister, he continued to be involved in implementing the PSE.[5][7]
Dionne headed the national candidate list of Benno Bokk Yaakaar, the coalition supporting President Sall, in the July 2017 parliamentary election.[8] Following the victory of Benno Bokk Yaakaar, President Sall reappointed Dionne as Prime Minister on 6 September 2017.[9] After the abolition of the office of Prime Minister in May 2019, he became Secretary General of the Presidency of Senegal, from 6 April 2019 to 28 October 2020.[3]