Platinum is Lambert's fifth album and sold 180,000 copies in its first week, ending June 8, Nielsen SoundScan said.
Lambert is the 11th female country artist to earn a top spot on the Billboard 200, and she's the first to find the top spot on the list since Taylor Swift's Red in December 2012.
Platinum also earned Lambert her fifth-consecutive No. 1 debut on the Top Country Albums chart, Billboard reported.
The only other top 10 debut this week was 50 Cent's Animal Ambition, which debuted at No. 4 with 47,000 albums sold.