CNBC had reported Sunday that a deal was in the works.
The acquisition comes as Hershey doubles down on its efforts to move beyond its chocolate heritage. It is the latest in a string of snack deals, as Big Food looks to reach increasingly mobile diners.
"The acquisition of Amplify and its product portfolio is an important step in our journey to becoming an innovative snacking powerhouse as together it will enable us to bring scale and category management capabilities to a key sub-segment of the warehouse snack aisle," Hershey CEO Michele Buck said in a statement.
In addition to SkinnyPop, Amplify's snack brands include Tyrrells, Oatmega and Paqui.
News of the deal rocketed Amplify's stock by 70 percent to $11.95 a share in Monday's premarket trading. The deal values Amplify at $12 a share, a 71 percent premium to Friday's close.
The two expect annual synergies of about $20 million over the next two years from cost savings and portfolio optimization.
The deal, which is expected to be accretive to Hershey's financial targets, values Amplify at roughly 14.8-times 2017 adjusted earnings before interest, tax, depreciation and amortization, including the synergy savings.
The deal is one of the first big initiatives led by Buck, who became CEO this year. She was named to the role months after the owner of Reese's rebuffed a takeover bid from Oreo cookie maker .
Buck has spoken openly about plans to expand further into the U.S. snacking category, which IRI pegs at roughly $89 billion. Hershey CFO Patricia Little recently acknowledged in an investor call, "Nothing is as profitable [as our core products]... But we do need to expand our portfolio."
The sweetsmaker, which has focused on the term "snackfection" — a blurring of the line between sweet and salty snacks — recently launched Hershey's and Reese's popped snack mix and chocolate dipped pretzels.
Snacks have been a rare point of growth for food companies, as U.S. consumers increasingly favor their food on the go. Among snacks, salty bites such as popcorn and chips reign supreme, beating out candy, cheese and cookies.
Hershey has, like many of its peers, for years sought to dip into the category through a series of small acquisitions. It acquired beef jerky maker Krave Pure Foods in 2015 and the parent of "healthy" chocolate bar brand barkTHINS a year later.
It is difficult though to grow these small brands to a scale at which they can make an impact on a company that last year generated roughly $7.4 billion in sales.
More recently, large food companies have been making bigger bets on snacks, confronted with continued slow sales and an increasingly competitive retail environment. With few large snack brands available to make an impact, those with clout have fetched steep premiums.
Just within the past couple of months, Kellogg announced its $600 million acquisition of RXBar, and Mars invested in the parent company of Kind Bar at a valuation of $3 billion to $4 billion. On Monday, Campbell Soup announced plans to buy Snyders-Lance for $4.87 billion.
SkinnyPop's parent Amplify went public in 2015 after the brand quickly caught on with snackers attracted to its sunflower coated kernels. It has since sought to diversify, buying U.K. snack maker Tyrrells for roughly $391 million.
Its stock though has more than halved, as it has struggled to support these acquisitions and the leverage they left behind. Amplify has also faced increased competition and retailers who award scale.
JPMorgan Securities and Morgan Stanley served as financial advisors to Hershey, and Skadden, Arps, Slate, Meagher & Flom served as legal advisor.
Jefferies acted as the financial advisor to Amplify and Goodwin Procter LLP is acted as legal advisor.