Ethan Peck said it was "an incomparable honour" to be cast as the pointy-eared alien in TV show Star Trek: Discovery.
Peck, grandson of Oscar-winner Gregory, will join the show when it returns for its second season next year.
The 32-year-old celebrated by posting a photo of himself with Nimoy's family giving Spock's famous Vulcan salute.
Born in Los Angeles in 1986, Peck has experience when it comes to taking on characters associated with other actors.
His previous roles include Patrick Verona - Heath Ledger's character in 10 Things I Hate About You - in the TV version of that 1999 film.
Alex Kurtzman, Star Trek: Discovery's executive producer, said in a statement that Peck would "effortlessly embody Spock's greatest qualities".
Set before the events of the original 1960s TV series, the show can be streamed on CBS All Access in the US and on Netflix around the world.
Star Trek: Discovery pleases fans
Since making his first appearance on television in 1966, the forever logical Mr Spock has been seen in a number of different incarnations.
Join us as we boldly go and look at some of the other actors who have played the half-human, half-Vulcan icon.
Nimoy was already an established character actor when he was approached to play Spock in the original pilot for Gene Roddenberry's Star Trek series.
NBC didn't like the pilot much but decided to make the series anyway, jettisoning all the cast apart from Nimoy.
The role of the USS Enterprise's unflappable science officer made Nimoy a star. But it was also one he found hard to shake off and move on from.
"The question was whether to embrace Mr Spock or to fight the onslaught of public interest," he wrote in a 1975 autobiography called I Am Not Spock.
Ultimately he chose the former, playing Spock again in the Star Trek films - two of which he directed - as well as the Next Generation TV series.
Nimoy died in 2015 at the age of 83.
The decision to "reboot" the Star Trek film series in 2009 called for a younger version of the Spock character, and a younger actor to play him.
That man was Zachary Quinto, who at the time of his casting was best known for playing the evil Sylar in TV series Heroes.
Quinto threw himself into the part, shaving his eyebrows and having his fingers glued together for scenes in which he gave the Vulcan salute.
The actor, now 41, was seen again as Spock in Star Trek Into Darkness (2013) and Star Trek Beyond (2016).
JJ Abrams' Star Trek film certainly did not want for Spocks. In addition to Quinto, it also saw Leonard Nimoy return to his signature role.
Then there was teenaged actor Jacob Kagan, who played him in scenes depicting Spock's troubled childhood.
Kagan, now 23, said he was "super psyched" to get the part, calling it "the opportunity of a lifetime".
"To get into character I watched a bunch of the old Star Trek episodes, and JJ Abrams was AMAZINGLY helpful with acting advice," he revealed in a 2012 webchat.
The Other Young Spocks
Spock died at the end of Star Trek II: The Wrath of Khan, heroically sacrificing himself to save Captain Kirk and the rest of the crew of the USS Enterprise.
"The needs of the many... outweigh... the needs of the few," he gasped before signing off with his deathless "Live long and prosper" catchphrase.
Spock didn't stay dead for long, returning in Star Trek III: The Search for Spock thanks to a regeneration that saw him grow from infant to adult at an alarming rate.
This required no less than four actors to share the role - Carl Steven, Vadia Potenza (above left), Stephen Manley (above right) and Joe W Davis.
The story ended with Nimoy, who also directed the film, back in the pointed ears, to precisely nobody's surprise.
In one sketch, Nimoy was seen proving his versatility by reeling off some of his most famous roles - "Spock Who, Mr Spock, Science Officer Spock, Captain Spock and now Admiral Spock."
"I am a fine actor of repute and standing," his puppet was heard insisting in another programme. "Just listen to my Chekov!"
Star Trek fans will be able to guess what comes next.