The joint effort, first reported by Reuters earlier on Thursday, could prove difficult as descendants of former Campbells Soup Chairman John Dorrance own a combined stake of about 41 percent in the company.
Loeb's Third Point hedge fund and Strawbridge together own a 8.42 percent stake in the 150-year-old company, with Third Point holding 5.65 percent, according to the filing with the U.S. Securities and Exchange Commission.
Third Point said it believed a strategic review underway at Campbell would create "significant value" for shareholders if conducted properly. Third Point also said it may seek board seats if it feels that Campbell's directors have failed to do their job appropriately.
Campbell said its board "remains dedicated to delivering a go-forward strategy that will drive value for all shareholders," and that it would make its plans public later this month.
Campbell shares rose as much as 4 percent on the news that Loeb, whose fund occasionally pushes management of its portfolio companies to perform better, is involved. The stock closed up 0.7 percent at $42.28. Since January, it has dropped 12.7 percent.
The 56-year-old investor bought his stake in Campbell after Chief Executive Denise Morrison unexpectedly stepped down in May. She left after the company gave a bleak forecast for the year and said it would embark on a review of its many brands.
Rival activist shareholder Carl Icahn also considered an investment in Campbell, but decided against it because the family dynamics would make it tough to press for big changes, according to a source familiar with the matter. Icahn's office declined to comment.
Campbell's annual meeting was held early last November, which means that Third Point would have a relatively short period of time to nominate potential directors if Loeb plans to mount a board challenge later this year.
Loeb's $18 billion hedge fund has a history of making investments in food companies, including most recently Nestle SA, where it has been pressing management to spin off some units and streamline the portfolio.
Campbell in 2015 reorganized into three divisions, creating the Campbell Fresh unit after combining what was a packaged fresh division with soups sold to supermarket delis. But Campbell Fresh struggled, resulting in a two-year decline in organic sales.
Analysts have said that the most logical path for the company may be to separate its profitable but debt-laden snack business from its slower-growing soup business.
While Kraft Heinz Co considered an acquisition of Campbell in the past, it is not currently exploring a bid, according to a source familiar with the matter. Kraft Heinz did not respond to a request for comment.
(Reporting by Svea Herbst-Bayliss and Greg Roumeliotis in New York; Editing by Tom Brown and Richard Chang)
By Svea Herbst-Bayliss and Greg Roumeliotis