Mr Mason will stay in post until Friday October 22, giving him time between then and Christmas to expand a Dementia Cafe he helped launch in 2018 before starting his next role.
Chair of Welcome to Yorkshire, Peter Box CBE, said: “We would like to thank James for the commitment and energy he has demonstrated during a particularly turbulent time for tourism and for the organisation.
"When James joined as chief executive almost two years ago there were many challenges to deal with.
"A positive plan was put in place to continue showcasing Yorkshire to the world and despite the Covid-19 pandemic adding a new and unexpected level of challenges for the tourism industry, James tackled all issues head-on and worked tirelessly.
"He embraced all aspects of the role passionately and with creativity.
"A board meeting will be arranged to discuss the next steps for Welcome to Yorkshire.
"We would like to wish James and his family well for the future.”
James Mason said he was honoured to have held the position and to have led a team of talented hard-working people.
"I’d like to express my gratitude to them all along with the many wonderful people across Yorkshire I’ve met in this role," he said.
"It has been a privilege to work with you all, to promote Yorkshire to the world and stand shoulder to shoulder with you through a pandemic.
"I only wish the organisation well going forward and most importantly the thousands of businesses that make Yorkshire so unique.
“While working under difficult conditions at times, there is lots we can be proud of, such as the much-loved Walkshire campaign, the launch of a personal membership and tree planting scheme, as well as the implementation of a Tourism Recovery Plan.
"The brief when I joined was to guide Welcome to Yorkshire towards steadier waters and drastically reduce costs.
"We achieved this despite all the restrictions we faced and never stopped innovating or striving for excellence.
"I’d like to thank everyone for their involvement in trying to bring the Tour de Yorkshire back especially our local authority partners with their continued commitment.
"These high-profile events will return to the region when the time is right.
“The decision to leave wasn’t an easy one as I have really enjoyed the role it but I’m excited about putting my energy into my new role.
"I will of course be committed to Welcome to Yorkshire and the staff until I leave before investing some time expanding Bradford Memories, a dementia group supporting individuals and their families living with the disease, as my mother does.
"Who knows, perhaps we can launch Yorkshire Memories.
"Watch this space… "