"You will have my support because you have no other option but to succeed. Failure is not an option, we have a country to look after," Ruto told the new ministers at the event in Nairobi.
The 22-member line-up will be tasked with tackling the cost of living crisis and other economic issues in the East African country, the cornerstone of Ruto's election campaign promises.
Musalia Mudavadi, a former vice president who broke ranks with defeated presidential candidate and opposition chief Raila Odinga to back Ruto, assumed the newly-created position of prime cabinet secretary.
The 62-year-old will be the most senior government minister and answer directly to the president and his deputy.
Alfred Mutua, a former governor whose party also sided with Ruto, will take charge of the foreign ministry.
Kithure Kindiki, a lawyer who served on the legal team that defended Ruto's August election win in court, will head the powerful interior ministry.
A law professor, Kindiki also represented Ruto at his trial at The Hague-based International Criminal Court for his alleged role in orchestrating the 2007-2008 post-election unrest that killed at least 1,100 people and displaced more than 600,000.
Former central bank governor Njuguna Ndung'u is the new treasurer.
Ruto vowed to run an inclusive, transparent and accountable government as he aims to transform the regional powerhouse.
"We have no grey areas, we have nothing to hide. We want to serve the people of Kenya," he said.
However, the new cabinet did not achieve the gender parity Ruto had promised on the campaign trail, naming just seven women to the team.