Jefferies' shares rise $2.00, or 14 percent, to close at $16.27 on Monday.
On Monday, Leucadia National Corp. said it may spin off its Crimson Wine Group before the Jefferies' deal is complete.
Once the transaction closes, Jefferies' four independent directors will join Leucadia's board, which will boost the board's size to 14 members.
Morningstar analyst Michael Wong said the deal is both a sound defensive and offensive move for Jefferies.
"Being a part of Leucadia with its diversified portfolio of companies and relatively strong balance sheet gives Jefferies fairly firm backing," he said in a note to investors. "The timing of this deal seems appropriate given the risk of a U.S. fiscal cliff and re-emerging European debt concerns."
For Leucadia, he said, the transaction is "transformational" but not as positive for investors.
Ratings agencies Moody's Investors Service, Standard & Poor's Rating Services and Fitch Ratings said that they are reviewing Leucadia's ratings for a possible upgrade. Fitch said that if the Jefferies' deal closes and there are no adverse credit developments, it is likely that Leucadia's issuer default rating will go to investment grade status from junk status. Standard & Poor's said that its issuer credit rating for Leucadia may also move to investment grade status from junk.
Leucadia fell 66 cents, or 3 percent, to close at $21.14.