On a nerve-jangling final night of a long Spanish league season, second-placed Real Sociedad won 3-0 at home to Atletico Madrid to ensure that nothing less than victory would be good enough for Real Madrid.
With Real leading 2-1 at halftime in Madrid that was far from a formality, but a second strike from Ronaldo just past the hour mark gave them the breathing space they needed.
Real Madrid coach Vicente del Bosque had the luxury of substituting Ronaldo to an ear-splitting ovation in the closing minutes before his side were crowned champions amid a spectacular firework display at the Santiago Bernabeu stadium.
Real Madrid finish the season with 78 points from 38 matches, two points ahead of runners-up Real Sociedad.
"We have suffered enormously over the course of the year and only after the third goal could we really relax," said Real's sporting director Jorge Valdano.
"The league is always important and very difficult to win and that's why we are so delighted."
SECOND PLACE
While Real Madrid were celebrating their second league title in three years, Sociedad had to settle for second place despite a comfortable 3-0 win at home to Atletico with goals from Darko Kovacevic, Javi de Pedro and Nihat Kahveci.
Their consolation will be a place in the group stage of the Champions League, a remarkable achievement in itself after three years spent struggling against relegation.
Deportivo Coruna, with 72 points, and Celta Vigo, on 61, were already assured of finishing third and fourth and taking the remaining Champions League places..
Last season's champions Valencia finished fifth on 60 points and go through to the UEFA Cup first round.
In the only other outstanding issue of the league season, Barcelona pipped Athletic Bilbao to a UEFA Cup place with a 2-0 win at home to Celta that took them up to sixth on 56 points.
Juan Pablo Sorin headed in the first for Barca on eight minutes and just after the break Javier Saviola wrapped up victory for the Catalans, who thus preserve their record of never missing a season of European competition.
Recreativo Huelva, Alaves and Rayo Vallecano were already relegated ahead of the final day, to be replaced by Murcia, Albacete and Real Zaragoza from division two.
VICTORY NEEDED
Real Madrid went into the last weekend of the season needing victory over Bilbao or a slip-up from Real Sociedad.
Del Bosque's side got the start they wanted when Luis Figo found Roberto Carlos in space down the left. The Brazilian turned the ball back in for Ronaldo, who struck left-footed while leaning back to open the scoring.
Raul had two good chances to add to the tally before Bilbao got their equaliser, a Bittor Alkiza strike that squeezed inside the near post.
Real looked rattled but recovered their poise when Ronaldo was brought down on the edge of the box in first-half injury time and Roberto Carlos cracked in a low free kick.
Real Sociedad went in level at halftime after a goalless first period but pulled clear of Atletico just after the break to put the pressure on their title rivals.
Real Madrid were ahead but looking far from comfortable until Ronaldo took a pass from Zinedine Zidane and smashed in his second goal of the game.
Real Madrid's victory secures yet another triumph for unassuming coach Vicente del Bosque, who has now guided them to two league titles and two European Cups since he took charge in November 1999.
