Lawmakers in the upper house are set overwhelmingly to approve the handover of the crown to the blue-eyed 46-year-old former Olympic yachtsman, who stands nearly two metres tall.
At the head of a new generation of royals, and with his glamorous wife Letizia, 41, a former television presenter, on his arm, the new monarch is riding high in the polls but faces a formidable task ahead.
As king, Felipe must restore the image of the monarchy after his father's reign became bogged down in scandal; inspire a people suffering from a 26-percent unemployment rate; and try to unite the nation even as the northeastern region of Catalonia seeks an independence referendum this November.
It is one of the last parliamentary acts before Spain says farewell to the 76-year-old King Juan Carlos and his wife Queen Sofia, who guided the country from dictatorship to democracy in a nearly 39-year reign.
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The outgoing king hosts the last official lunch of his reign today for senior figures of state including Prime Minister Mariano Rajoy.
Tomorrow, Juan Carlos will sign the act of parliament formalising his abdication.
Felipe will be sworn in before both houses of parliament on Thursday morning.
In celebration, the new king and the queen -- whose dress for the ceremony remains a closely guarded secret -- will be driven through the broad avenues of central Madrid.
The royal couple, who have two blonde-haired daughters -- eight-year-old Leonor, who will be the youngest direct royal heir to the throne in Europe, and seven-year-old Sofia -- will also appear before the crowds on the front balcony of the Spanish capital's old Royal Palace.