Image source, PA MediaEnergy minister Graham Stuart has stood down from the government.
The Beverley and Holderness MP said he wanted to focus on local issues after serving in various ministerial posts over eight years.
In his resignation letter, Mr Stuart said "we have achieved a lot in driving the energy transition",and the prime minister had his full support.
He has been replaced by Justin Tomlinson, a former minister and deputy Tory chairman.
In other changes, Minister of State for Development and Africa Andrew Mitchell has been given the additional title of Deputy Foreign Secretary.
With Foreign Secretary David Cameron in the House of Lords, Mr Mitchell has routinely answered questions on his behalf in the Commons.
Minister for Disabled People Mims Davies has been promoted to be a minister of state in the Department for Work and Pensions.
Mr Stuart attended Cabinet under Liz Truss, and previously served as Europe minister and as a trade minister.
In his letter to Mr Sunak, Mr Stuart said: "I'm proud of all we have achieved as a government, not least being the first major economy to halve CO2 emissions.
"Under your leadership the UK is at near full employment, has inflation falling fast and is set to go from strength to strength in the coming years."
Serving as a minister had been an "enormous privilege", he added.
Mr Stuart, who had a majority of 20,448 over the Labour candidate in the 2019 general election, made clear that he intended to fight Beverley and Holderness in the next election expected later this year.
In an earlier statement, he said he wanted to concentrate on issues such as making roads safer, broadband delivery, improving access to dentistry and healthcare, working with farmers on flooding, and increasing the number of defibrillators in his constituency.
Mr Stuart listed his achievements since first being elected to Parliament in 2005 as including helping to install rock armour to protect the coastline at Withernsea, saving East Riding Community Hospital, introducing life-saving defibrillators in rural communities, and cutting fares on the Humber Bridge.
Last month, two other ministers resigned on the same day – armed forces minister James Heappey and education minister Robert Halfon.
Liberal Democrat deputy leader Daisy Cooper called for a general election now, saying: "The drumbeat of Conservative resignations is becoming deafening.
"Even Rishi Sunak's ministers know that time is up on this tired and out of touch government."