The order, with a cumulative value of $18 billion, is the single largest commercial airplane order in Boeing's history by dollar value.
It also makes 2011 the best-selling year for the 777 programme, surpassing the previous record of 154 orders in 2005.
With the Emirates order, the net order book for the 777 in 2011 currently stands at 182.
The options for 20 additional airplanes are valued at $8 billion, a statement released on Sunday said.
"The 777's reliability, performance and operating economics have firmly established it as the backbone of our fleet," said Emirates Airline & Group chairman and chief executive Sheikh Ahmed bin Saeed Al Maktoum.
"We have an ambitious and strategic plan to continue growing our international network and especially increasing our long-haul, non-stop routes.
"This order supports our fleet expansion and reiterates our commitment to operating a modern fleet for the benefit of our passengers and to ensure operational efficiency as well," he said.
Emirates is the world's largest 777 operator, with a fleet of 94 777s through direct purchase and lease, plus additional unfilled orders on backlog for 41 777-300ERs previously on order.
It is also the only airline in the world to operate every model in the Boeing 777 family, including the 777 Freighter.
Emirates took delivery of its first Boeing 777 -- a 777-200 -- in 1996 and since then, the airline has deployed the 777 on short, medium and long-haul routes.
The 777-300ER airplane carries 365 passengers up to 7,930 nautical miles (14,685 km). Boeing incorporated several performance enhancements for the 777-300ER, extending its
Dubai offers special Diwali fares for India destinations
IMAGES: Amazing interiors of Boeing's business jet
IMAGES: The making of the Boeing 787 Dreamliner