The actor, 78, confirmed this weekend that he was set to "explore new dimensions" with the captain.
The new series from CBS All Access will tell the story of the next chapter of Picard's life.
Sir Patrick played the character on TV and in films from 1987 to 2002 and said on Twitter that he had thought that final appearance as Picard, in the movie Star Trek: Nemesis, was his last.
He told his 3.13 million followers on the site: "I will always be very proud to have been a part of Star Trek: The Next Generation, but when we wrapped that final movie in the spring of 2002, I truly felt my time with Star Trek had run its natural course.
"It is, therefore, an unexpected but delightful surprise to find myself excited and invigorated to be returning to Jean-Luc Picard and to explore new dimensions within him.
"Seeking out new life for him, when I thought that life was over."
Sir Patrick went on: "During these past years, it has been humbling to hear stories about how The Next Generation brought people comfort, saw them through difficult periods in their lives or how the example of Jean-Luc inspired so many to follow in his footsteps, pursuing science, exploration and leadership.
"I feel I'm ready to return to him for the same reason - to research and experience what comforting and reforming light he might shine on these often very dark times.
"I look forward to working with our brilliant creative team as we endeavour to bring a fresh, unexpected and pertinent story to life once more."
An air date has yet to be announced.