NEW YORK — Morgan Stanley is buying the investment management firm Eaton Vance in a deal valued at about $7 billion.

Eaton Vance, based in Boston, has more than $500 billion in assets under management.

Morgan Stanley Chairman and CEO James P. Gorman said in a prepared statement today that Eaton Vance will add more fee-based revenues to its investment banking and institutional securities franchise. The deal will give Morgan Stanley’s investment management arm approximately $1.2 trillion of assets under management and more than $5 billion of combined revenues.

Eaton Vance shareholders will receive $28.25 per share in cash and 0.5833 of Morgan Stanley common stock, or approximately $56.50 per share. Based on the $56.50 per share, the amount paid to Eaton Vance shareholders will consist of about 50% cash and 50% Morgan Stanley common stock.

Each Eaton Vance shareholder will have the option to choose all cash or all stock, subject to a proration and adjustment mechanism. Eaton Vance shareholders will receive a one-time special cash dividend of $4.25 per share to be paid before the transaction’s closing by Eaton Vance to its shareholders from existing balance sheet resources.

The deal is expected to close in the second quarter of next year.

Shares of Eaton Vance spiked 43% before the opening bell.