An elated Rotich in an interview with The Standard said that he was happy and grateful for the appointment to the key position.
"I am happy and thank the Head of State for his appointment and the confidence he has in me. I am committed to giving his government the best I can in my service," he said.
He said that the appointment by the Head of State coming after the court acquittal had fully vindicated him and helped to erase every iota of imagination in Kenyans' minds that he had any valid corruption case.
"After the courts, President Ruto's appointment is a complete vindication of the former government's attempt to malign my name unnecessarily," said Rotich.
Following the charges, the former CS pleaded not guilty to all counts of corruption, financial misconduct, and abuse of office.
In 2019, Rotich was charged alongside other senior officials including former Treasury Principal Secretary for alleged involvement in the misuse of public funds allocated for the projects. Rotich maintained that no money was lost in the Arror and Kimwarer dams' deal.
He said he wondered where the alleged proceeds of the stolen cash might be because he did not have any foreign accounts.
As Ruto's Senior Advisor on Fiscal Affairs and Budget Policy, Rotich will be based at the State House putting him at the centre of the economic planning and policy formulation, debt management, and the implementation of the government's ambitious Bottom-UP - Economic Agenda.
For close to eight years, the former CS was at the helm of the National Treasury before being befallen by what he termed a political witch-hunt during President Uhuru Kenyatta's government .
The Havard-trained economist born in 1969, in Kimwarer, Elgeyo Marakwet county was plucked by Uhuru from the Treasury where he was the Head of Macroeconomics to head the National Treasury.
He holds a Master's degree in Public Administration (MPA) from Harvard University, another Master's degree in Economics, and a Bachelor of Arts Degree in Economics and Sociology from the University of Nairobi.
As a senior advisor on fiscal affairs and budget policy, a position the current Central Bank of Kenya Governor Kamau Thugge held before he moved to CBK, Rotich will hold a pivotal role in advising the president on matters about fiscal policies and budget management.
He joins other Ruto economic advisors including former CS Aden Mohamed currently Chief of Strategy Execution, Executive Office of the President, and Chairman of the Presidential Council of Economic Advisor David Ndii , and Senior Advisor & Head of Economic Transformation Secretariat Augustine Cheruiyot
Rotich will be tasked with the development and analysis of the budget which includes auditing the financial implications of proposed policies, scrutinizing government revenues and expenditures, and forecasting deficits and debt levels.
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He will also provide the foundation for informed decision-making regarding budget allocations and fiscal priorities.
Additionally, the former CS will be expected to conduct economic evaluations to gauge the impact of various fiscal measures on the overall economic landscape.
After his 'incarceration,' Rotich said that he had never spoken with his former boss Uhuru since his tribulations started.
"I have not spoken to Uhuru Kenyatta since I was arrested, nor has he called me. I have nothing to say to him at the moment. He might have kept away from me despite us working together in the past. He might not have wanted to deal with people who had been charged," he said in the interview with The Standard.
He said the charges against him were meant to "to achieve extraneous political interests as opposed to the real matter of the case as presented in court."
Rotich claimed that there was a choreographed campaign to have him face 19 charges and that leaders from across the political divide used the matter during public rallies to advance their selfish political goals.
He had questioned advice given to Uhuru to allow 28 people to be charged. He was acquitted last week of 19 charges, which included conspiracy to defraud the government, and violation of the Public Finance Management Act.
The former CS said that "it was clear that games were being played by the Directorate of Public Prosecutions since it was fishing for evidence".
Rotich said that it was interesting to be told that he had conspired with people that he had not met to defraud the government.
"Majority of the witnesses were from Kerio Valley Development Authority. I do not know them. Those at the Treasury we worked together before turned against me," he said.