Prince William is to leave the military after more than seven years of service, Kensington Palace has announced.
The Duke of Cambridge completed his final shift as an RAF search and rescue pilot on Tuesday.
He will now focus on royal duties and charity work together with the Duchess of Cambridge, a palace spokesman said.
The Duke and Duchess of Cambridge and Prince George are expected to move from their Anglesey home to Kensington Palace within the next few weeks.
BBC royal correspondent Peter Hunt tweeted that royal officials said the next 12 months would be "transitional" for Prince William. He will not become a "full time royal" at this stage, they said.
The duke, with the Duchess of Cambridge, will continue to support the work of the Queen and the Royal Family through a programme of official engagements - both at home and overseas, the palace added.
He plans to expand his work in the field of conservation, particularly in respect of endangered species, through the Royal Foundation of The Duke and Duchess of Cambridge and Prince Harry.
The foundation has partnered with seven of the world's most influential conservation organisations under United for Wildlife, a long-term commitment to preserve the world's natural resources.
Prince William said: "The threats to our natural heritage are extensive, but I believe that this collaboration of the best minds in conservation will provide the impetus for a renewed commitment and action to protect endangered species and habitats for future generations.
"At the root of the illegal wildlife trade, for example, is the demand for products that require the deaths of tens of thousands of these animals every year, pushing them further towards extinction.
"We must work together to prevent this catastrophe and allow our children the opportunity to experience wildlife in its many beautiful and varied forms."
The duke recorded two public messages in London on Thursday focusing on reducing demand for rhino horn and ivory. They will air globally later this year.
The duke and duchess attended the inaugural Tusk Conservation Awards at the Royal Society in London on Thursday evening.
In a speech to guests, Prince William started by joking about spending his first night away from baby son Prince George.
"As you might have gathered, Catherine and I have recently become proud parents - of a baby who has a voice to match any lion's roar," he said.
"This is actually our first evening out without him, so please excuse us if you see us nervously casting cheeky glances at our mobile phones to check all is well back home.
The duke continued: "Like any new parents, our thoughts inevitably turn to the world that our child will inherit.
"It is unfathomable to imagine a world in which children who have been born in the past couple of months may grow up in a world in which rhinoceros have ceased to exist in the wild."
The palace said the duke was considering a number of options for public service and will make a further announcement in due course.
Tuesday's final RAF shift brought to an end a three-year posting on Anglesey for the prince.
In an interview for the BBC Wales documentary Helicopter Rescue, he said: "There's no greater feeling than when you've actually done some good and saved someone's life.
"I don't think there's any greater calling in life... to be able to see a son or daughter's face when you bring their mother or father back from the edge of death - it's quite powerful."
The head of the RAF, Air Chief Marshal Sir Andrew Pulford, praised the duke's work in the air force.
Sir Andrew said Flight Lieutenant Wales had been an "integral" part of the RAF's search and rescue force, "often in the most demanding of conditions, [he] has contributed directly to saving lives in the mountains of North Wales and from the ravages of the Irish Sea.
He added: "He has earned the respect of all who have worked with him as a highly professional and competent pilot."
In a speech at the Anglesey Show in August, the duke thanked the island's people for being so welcoming to him and his wife.
"I know that I speak for Catherine when I say that I have never in my life known somewhere as beautiful and as welcoming as Anglesey," he said.
"I know that both of us will miss it terribly when my search and rescue tour of duty comes to an end next month and we have to move elsewhere.
"From the bottom of my heart, thank you for making my wife and me so welcome when we arrived here, as you do thousands of visitors each year."
He said the island had been their first home together and would always be an "immensely special place for us both".
Though their main home will be the newly refurbished Kensington Palace, the royal couple are also expected to take up their country retreat Anmer Hall on the Queen's private Sandringham estate in Norfolk later this year.