The company said it sold 2.11 million handsets in a 12-hour flash sale held to celebrate its fifth anniversary, the South China Morning Post reported on Thursday.
The half-day bonanza, which brought in 2.08 billion yuan ($335 million) from sales of handsets and other accessories broke the previous record held by Alibaba's Tmall, which sold 1.89 million handsets in November during a 24-hour event.
"This is beyond my imagination," chief executive Lei Jun told reporters at the company's headquarters in Beijing.
The new record has been certified by the official Guinness World Records and examined by auditor PricewaterhouseCoopers, he said.
Festive offer on Xiaomi phones
Xiaomi easily broke their record from the same event last year, which saw them selling 1.3 million smartphones.
Mobile phones and other accessories sold during the 12-hour event, dubbed "Mi Fan Festival", were discounted from Xiaomi's already famously low prices.
In addition to smartphones, the company said it sold 38,000 televisions, 200,000 fitness bands, and 247,000 of its brand new "smart" power strips -- a sign that it was gaining traction in its efforts to expand beyond its core business.
In 2014, Xiaomi sold 61 million smartphones and had a revenue of 74.3 billion yuan, becoming the world's number three smartphone player and China's top smartphone brand, overtaking Apple and Samsung.
The company was valued at $45 billion in a December funding round that drew investors ranging from Singapore's sovereign wealth fund to a private capital firm backed by Alibaba Group co-founder Jack Ma.
