The Croatia international has claimed two Champions League titles, a King's Cup, UEFA Super Cup and the Club World Cup since joining from Tottenham Hotspur in 2013 for a fee of 35 million euros (£31.17 million).
But the domestic league crown, which Real last won in 2012, has eluded him.
"I've won everything since I arrived apart from La Liga. You could say our priority is to win the league this year because four years without it is too long," Modric told a news conference.
His influence at the club has grown each year after initially being questioned over his price tag -- in December 2013 readers of Spanish newspaper Marca voted him the worst signing of the season.
The 31-year-old has won over the notoriously impatient Real supporters who gave him a rapturous reception after scoring during a stunning display in a 5-2 win over Osasuna last month.
"The criticism didn't hurt me. I knew I had come to the biggest club in the world, where the demands are huge -- I was prepared for that," said Modric.
"I didn't start well but I never doubted, I knew I would succeed sooner or later.
"Today is a special day. I promise I'll give everything and will work hard to match the club's demands. I hope to have many more successes here," added Modric.
"I hope this isn't my last contract renewal. My wish and desire is to end my career at Real."
Modric missed Tuesday's 5-1 Champions League win over Legia Warsaw with a knee injury sustained last month against Borussia Dortmund.
He is expected to be back next month although the player could not put a specific date on his return.
(Reporting by Richard Martin; Editing by Tony Jimenez)
