Kardashian's publicist, Ina Treciokas, confirmed Tuesday that the couple are engaged.
E! News first reported that West proposed to Kardashian Monday - her 33rd birthday - in front of family and friends at the AT&T Park, home of the San Francisco Giants.
Kardashian gave birth to the couple's first child, daughter North West, in June.
A photo posted on Instagram shows a screen at the stadium that reads "PLEEEASE MARRY MEEE!!!" - in typical West font - above a black-clad orchestra. Another shows Kardashian showing off a diamond ring with a smiling West behind her.
The Kardashian clan has a series of reality shows on E!, but the network said Tuesday it did not have cameras at the stadium to capture the moment.
Khloe Kardashian seemed to celebrate on Twitter when she wrote: "Tears of JOY!!!!!!! Wow!!!!!!" She also tweeted: "Wow!!!!! Am I dreaming-!?!" Kimye were quiet on Twitter.
Kardashian was previously married to NBA player Kris Humphries. Their divorce was finalized in June after they were married for 72 days in 2011. Her first marriage was to music producer Damon Thomas in 2000.
West is currently on a tour with Kendrick Lamar. "The Yeezus Tour" will visit the SAP Center in San Jose on Tuesday night. Earlier Monday, he attended the Hollywood Film Awards in Beverly Hills, presenting Steve McQueen with the Hollywood Breakout Director Award.