Sag-Aftra reached agreement with the Alliance of Motion Picture and TV Producers (AMPTP) in a unanimous vote.
The shutdown - combined with a separate writers' strike - paralysed the entertainment industry and disrupted numerous major films and TV shows.
Actors have been calling for better pay and safeguards on the use of AI.
Sag-Aftra president Fran Drescherposted: "We did it!!!!" She thanked members "for hanging in and holding out for this historic deal!"
Actors have welcomed the deal, with Zac Efron describing it as "incredible" at the premiere for his wrestling film The Iron Claw.
Efron's co-star Jeremy Allen White, who stars in TV drama The Bear, found out the strike was over during an interview on the red carpet with Entertainment Tonight. "That's amazing!" he exclaimed.
Oscar winnerOctavia Spencer wrote on social media: "Who else is dancing right now??? Ready to work now that the strike is over! Congratulations and thank you to our @sagaftra negotiating committee!"
Jamie Lee Curtis posted on Instagramthat "perseverance pays off".
This Is Us starMandy Moore said on her Instagram story: "Let's get back to work, friends!"
She added: "Thank you @sagaftra negotiators and leadership for getting us over the finish line!!! Gratitude is the attitude!!"
Alec Baldwin offeredhis "congratulations to everyone who did this great work on behalf of the members", in a post on Instagram.
Sag-Aftra chief negotiator Duncan Crabtree-Ireland told Reuters there were "definitely some tears, a lot of big smiles, a lot of hugs" when the agreement was reached.
The three-year contract would "make a long-term difference for the future of our members in this industry", he said.
The union said the deal was valued at more than $1bn (Â£814m) and included increases in minimum salaries, a new "streaming participation" bonus, and more protections against their images and voices being replicated by artificial intelligence.
Sag-Aftra said the strike would officially end on Thursday, with more details released following a meeting on Friday.
Union negotiating committee member Kevin E Westtold Varietythat there were "tears of exhilaration and joy" after the contract was approved, but that the agreement was "not perfect".
Fellow committee member Shaan Sharmatold the New York Timeshe had mixed emotions because not all of the union's demands were met.
"You can be happy for the deal overall, but you can feel a sense of loss for something that you didn't get that you thought was important," he said.
AMPTP said it was pleased to have reached the tentative agreement and "looks forward to the industry resuming the work of telling great stories".
It said the deal gave Sag-Aftra "the biggest contract-on-contract gains in the history of the union".
In addition to increased pay and AI guarantees, Sag-Aftra has called for increased royalties and higher contributions to actors' pension and health plans.
Sag-Aftra represents about 160,000 members and has been on strike since July 14, causing major disruption and knock-on effects for those in all branches of the film and TV industry, and in countries like the UK as well as the US.
Disney/Marvel's Blade, Dune: Part Two and Fantastic Four have all been delayed by several months, while Avengers: The Kang Dynasty and Avengers: Secret Wars have also been pushed back by a year.
Live action remakes of Disney animations Moana and Lilo & Stitch have also been affected, as has James Cameron's Avatar series and Paddington in Peru.
As well as film delays, Hollywood stars have also not been attending some events such as premieres while the strike has been taking place, as union rules prohibit them from taking any work, including promotion or publicity for projects.
Some productions, like The Iron Claw, had an "interim agreement", meaning stars could do interviews and attend the premiere.
Actors had also not been allowed to attend awards ceremonies, meaning the Emmys - TV's biggest night - were delayed from their usual September slot.
The Emmys ceremony will take place in January instead, and organisers of events like the Oscars are likely to be breathing a sigh of relief that stars can hit the red carpet when the movie awards season kicks off in the New Year.
The Writers Guild of America (WGA)ended its separate strike in September, after almost five months.
The combination of the actors' and writers' strikes is estimated to have cost the California economy more than $6.5bn (Â£5.3bn) so far, according to Deadline.
Los Angeles Mayor Karen Bass welcomed the "fair agreement", and said the strikes had impacted "millions" in Los Angeles and throughout the country.
Although Hollywood's star actors earn millions of dollars, many lesser-known performers often struggle to get by, particularly amid rising inflation and industry changes.
US actors are expected to resume work after their union agreed a tentative deal with Hollywood studios to end a four-month strike.