Fadoul has served as interim finance minister since Deby sacked his predecessor, Christian Georges Diguimbaye, last month. The appointment comes amid stalled negotiations with Glencore over more than $1 billion in oil-backed loans Chad owes the commodities trader.
Glencore lent the West African country's state oil firm SHT about $1.45 billion (£1.1 billion) in 2014 to be repaid with crude oil. The loan was subsequently syndicated with several banks.
It was restructured in 2015 following the crash in global oil prices but Chad is again struggling to repay the debt. Funds from the International Monetary Fund depend on reaching new terms.
In October, Chad decided to redirect crude previously allocated to Glencore in a marketing agreement to Exxon Mobil instead starting from January, which has made negotiations fraught.
Djimet Arabi, an adviser to Deby, was named the new justice minister in the reshuffle while Ahmadaye Abdelkerim Bokit takes over the security ministry.
The new foreign minister is Mahamat Zene Cherif, Chad's former permanent representative to the United Nations.
(Reporting by Madjiasra Nako; Writing by Aaron Ross; Editing by Dale Hudson)