He was officially confirmed following a vote at a full council meeting at County Hall.
Coun Smith, who represents Newark East and was previously cabinet member for education and SEND, replaces Coun Ben Bradley who has stepped down for family and personal reasons.
The new leader said he is honoured and privileged to be elected and has spoken about his priorities for Nottinghamshire residents.
He said: “I am absolutely delighted to be elected leader of Nottinghamshire Council and I am looking forward to working tirelessly to deliver on key priorities for people across the county.”
Coun Smith highlighted the county council’s ‘great’ record of delivering services and spoke of the ‘challenging’ outlook facing all local authorities.
He said: “One of my first priorities will be balancing the budget in February 2025 and we have an excellent record in delivering well-run, efficient services while keeping council tax low.
“I am proud that we are one of a few local authorities that have not closed a single library, maintained a thriving youth service and have expanded rural bus services with our Nottsbus OnDemand.
“We have invested more than £100m in our capital programme and have ploughed millions of pounds into improving our roads, as well as delivering on our commitment to build schools and improve the standards of education across the county.”
In his previous role as cabinet member for education and SEND, Coun Smith said he would remain focussed on his commitment to hit the government’s 50 per cent target of Educational, Health and Care Plans (EHCP) timescale by the end of the academic year.
He stressed that as leader he would continue to lobby the Government on SEND issues.
He will announce his successor as cabinet member for education and SEND in the coming days.
The new leader will also be a loud voice for a fair Local Government Settlement, due to be announced on December 23, through his work with the County Councils Network, Local Government Association and the East Midlands Combined County Authority (EMCCA).
Coun Smith said: “As a board member on EMCCA, I will be banging the drum for Nottinghamshire on transport, infrastructure, skills and investment funding for and I look forward to working closer with the mayor in these key areas.
“There are projects like STEP Fusion in Bassetlaw, which will provide thousands of highly skilled jobs for Nottinghamshire residents, including hundreds of apprenticeships for young people.
“Key infrastructure projects require the backing of the Mayor and our local MPs and I will be knocking on their doors regularly to fly the flag for funding across Nottinghamshire.
“For me it’s about delivery, delivery, delivery for Nottinghamshire residents as part of our ongoing drive to make our county a great place to live, work and visit.
“I hope I can maintain our proud record on the building and maintenance of schools, transport improvements, maintaining our library network and our fantastic youth service.”
Coun Smith thanked his predecessor Coun Bradley for his three-and-a-half years as leader, saying he hopes to build on his legacy.