The agreement wraps up a courtship that has lasted over three months and required AbbVie to increase its offer for the British company four times. The final indicative price of 53.19 pounds a share (based on the weighted average price for AbbVie shares over the last month) is around 50% over where Shire’s stock was trading before the news of AbbVie’s interest became public.

Even at the agreed price, Abbvie said in a statement that it expects the deal to add to earnings per share immediately, and to contribute over $1 per share in earnings by 2020. That’s equivalent to nearly 40% of last year’s EPS at AbbVie.

AbbVie said it will continue to be listed in New York.

It’s unclear how the tax implications of the deal will play out, after signs that the Obama Administration is now urging Congress to enact legislation immediately to stop such “inversion”-driven deals, whose primary aim to escape corporate income tax liability in the U.S.

The company said it expects the deal to reduce its effective tax rate to approximately 13%, afte around 22% in 2013.

However, regardless of the tax angle, the companies said Friday they believed in the logic of the tie-up, which will create a specialist in rare disease treatments with global reach, and with few overlaps.

“By combining AbbVie and Shire, we’re creating a unique, diversified biopharmaceutical company,” AbbVie chief executive Richard A. Gonzalez said.

Shire chairman Susan Kilsby said the combination represents “an exciting fit of two complementary businesses that will create a new market leader in specialty pharmaceuticals with a portfolio of fast growing products, a promising pipeline and enhanced growth prospects.”

The two companies will hold a conference call for investors at 0900 EDT Friday.