US District Judge Lewis Liman in Manhattan said Lively's claims to a California state agency about Baldoni's alleged harassment during the filming were privileged, and shielded from the defamation claim by Baldoni and his Wayfarer Studios.
Liman also dismissed Baldoni's related $US250 million ($A384 million) lawsuit against the New York Times for its December 21, 2024 article about the dispute, "'We Can Bury Anyone': Inside a Hollywood Smear Machine".
The judge said Baldoni can try to file a much narrower lawsuit against Lively focused on contractual issues.
"Today's opinion is a total victory and a complete vindication for Blake Lively," her lawyers Michael Gottlieb and Esra Hudson said in a joint statement.
"As we have said from day one, this $US400 million ($A614 million) lawsuit was a sham."
Baldoni's lawsuit was in response to Lively's own lawsuit over his alleged harassment. She still seeks unspecified triple and punitive damages, and a March 2026 trial remains scheduled before Liman.
A Times spokesman, Charlie Stadtlander, said in a statement: "Our journalists went out and covered carefully and fairly a story of public importance, and the court recognised that the law is designed to protect just that sort of journalism."
The feud began publicly in December when Lively filed a complaint with the California Civil Rights Department (CRD) about Baldoni, followed by her lawsuit.
In response, Baldoni's countersuit accused Lively, her husband and actor Ryan Reynolds, Lively's publicist Leslie Sloane, the Times and others of trying to smear him.
Baldoni said Lively tried to effectively hijack It Ends with Us, which he directed and whose themes included domestic violence, and then blame him when her "disastrous" promotional approach prompted an online backlash against her.
Lively had called Baldoni's lawsuit a "vengeful" attempt to weaponise the federal courts, and pursue a "sinister campaign to bury and destroy" her for speaking out.
The Times, meanwhile, said it shouldn't be punished merely for newsgathering, and said in the article that Baldoni led a "smear campaign" in retaliation for Lively's complaints was protected opinion.
Liman said Baldoni alleged at most that Lively communicated the privileged CRD complaint to the Times, while her husband and publicist made what they thought were true statements about Baldoni's sexual harassment.
"The Wayfarer Parties' conclusory allegations that the Lively, Reynolds, and Sloane engaged in a conspiracy to defame the Wayfarer Parties by disseminating knowingly false statements cannot substitute for factual allegations supporting a plausible inference that this occurred," the judge wrote.
"Freedoms of expression require breathing space, and a publisher must be permitted to publish the story that it believes in good faith to be before it," Liman wrote.
It Ends with Us garnered mixed reviews, but grossed more than $US351 million ($A538 million) worldwide, according to Box Office Mojo.Â
with AP
