Star Alliance member EgyptAir has signed a letter of intent covering a firm order for 12 CS300s plus purchase rights for another 12 of the 130-seat aircraft.
The US trade department imposed tariffs of 300% on the C Series as it upheld a complaint from Boeing over subsidies the aircraft received from the Canadian and United Kingdom governments.
Bombardier CEO Alain Bellemare told analysts two weeks ago that he expected sales of the C Series would accelerate following the deal with Airbus.
The CS300 is the larger version of Bombardier's C Series aircraft. Its presence is "adding confidence about the long-term success of the program", he said November 2.
Earlier this month an unnamed European airline said it meant to buy at least 31 of the C-Series planes.
The deal includes 12 additional aircraft with purchase rights.
The CS300 carries a list price of $89.5m, although discounts of 50% or more are common in the industry.
Through its recent agreement with Airbus, Bombardier plans to get around swingeing US tariffs on imports of the C Series by constructing aircraft at Airbus' US factory.
Bombardier and EgyptAir said they hoped to finalize the deal before the end of 2017, the statement added. Egypt civil aviation minister Sherif Fathy said in October that the government expected to pay about $3.3bn of the cost to acquire 45 aircraft.