The triumph extends Los Blancos' record haul to 34 league titles -- eight more than Barca, who had lifted the past two La Liga trophies.
Zinedine Zidane's team overhauled their rivals with a 10-game winning streak since La Liga returned in June after a three-month break due to the coronavirus pandemic.
Zidane -- who was reappointed for his second spell as coach in March 2019 -- has now won two trophies this year, after picking up the Spanish Super Cup in January.
The legendary ex-player was previously in charge from 2016 to 2018, winning 10 trophies including one league title and three Champions Leagues, before resigning.
The 2019-20 season has seen Madrid and Barca battle it out at the top of the table, with little to separate the two giants.
Madrid have had to compete for much of the campaign without €100 million star signing Eden Hazard, who has struggled with a persistent ankle injury that eventually required surgery.
The 2-0 Clasico win over Barca on March 1 was crucial -- but it was followed by a 2-1 defeat at Real Betis that left Barca two points ahead when La Liga was suspended on March 12.
Since the restart on June 11, Madrid have maintained a 100% record.
Setbacks due to the redevelopment of the Bernabeu -- such as the need to play home games at the Alfredo di Stefano stadium, home of Madrid's B-team Castilla -- have been dealt with, as has speculation about the futures of big-name players such as Gareth Bale and James Rodriguez, whom have both been sidelined by Zidane.
Meanwhile, Barca have been hit by a series of off-the-field distractions including speculation about the future of coach Quique Setien -- who replaced Ernesto Valverde in January -- and that of Lionel Messi, as well as financial pressure exacerbated by the pandemic.
Madrid veterans Sergio Ramos, 34, and top scorer Karim Benzema, 32, have made important contributions in attack, while Thibaut Courtois will win the Zamora trophy for the La Liga goalkeeper with the best goals-to-games ratio.
There will be no title celebrations, including the traditional bus parade to the Cibeles fountain, with club and local officials asking fans to stay at home over concerns about further outbreaks of the coronavirus.
Madrid will look to win another trophy this summer in the Champions League, as they try to overturn a 2-1 round-of-16 first-leg deficit against Manchester City on Aug. 7 to reach the final stages in Lisbon later that month.