Senior politicians spoke of their relief after Ineos, the site's owners, reopened the plant and its adjacent oil refinery, saving thousands of jobs.
Some 800 employees who gathered at yesterday's meeting cheered loudly as they were told their jobs - and many others at local businesses which rely on the plant - had been saved.
The move followed acceptance by the Unite union of a survival plan, including a pay freeze, ending of the final salary pension scheme and other changes to terms and conditions.
Ineos had earlier said it would close the site after workers refused to sign up to the changes.
The site had been shut down for the past week as a result of the dispute.
Pat Rafferty, Scottish secretary of the Unite union, said: "Relief will ring right round the Grangemouth community, and across Scotland today.
"Hundreds of jobs that would have been lost can now be saved and £300 million will be invested into the plant."
First Minister Alex Salmond said a "potential disaster" had been averted.
He added: "I am delighted that people have rallied round to protect these jobs, and now we can all agree that Grangemouth has an outstanding future."
Calum MacLean, Ineos chairman at Grangemouth, said there was a "very large" cheer from the staff who gathered at the meeting.
He added: "We deliberately wanted to make the announcement firstly to the employees because it's the employees that have had a horrendous week with the announcements that came out earlier."