The decision defied the expectations of both the British government and trade unions in Northern Ireland.
If the ITC finds in Boeing's favour, the tariffs will be applied, undermining around 1,000 in Belfast where the C Series wings are produced.
The independent, bipartisan trade organization voted unanimously against duties imposed by the U.S. Commerce Department in October.
Commerce ruled previous year that the Canadian firm had unfairly received government subsidies and sold its C series planes at artificially low prices in the United States.
The trade court said it hadn't found Boeing was materially harmed by Bombardier's trade practices. "We're happy to see that the ITC came to the right decision".
But the unanimous ITC decision, coming after preliminary rulings that pointed to steep tariffs, caught many analysts by surprise. Last year, with the plane's access to the US market in doubt, Bombardier agreed to hand control of the program to Airbus SE in exchange for the European planemaker's marketing muscle and manufacturing expertise.
The lone US customer, Delta Air Lines Inc., was originally expected to receive the first of its firm order for 75 CS100 planes in the spring, but now plans to wait until the aircraft are assembled in the United States.
Delta, the recipient of the Bombardier-made planes, wrote it was "pleased" with the ruling and pointed out that "Boeing offers no viable alternative" to the CS100 series planes from Canada.
The ruling comes after Theresa May met U.S. president Donald Trump at the World Economic Forum in Davos, Switzerland, on Thursday.
"I welcome the common sense approach from the ITC in rejecting the protectionist complaint brought by Boeing".
"They are the true market leaders", Conner said.
"The C Series is the most innovative and efficient new aircraft in a generation", the company said.
Chief on the list of US sales prospects is JetBlue Airways Corp., which earlier this year delayed a decision on updating its fleet of regional jets.
"Unite looks forward to continuing to work with Bombardier to secure future sales and investment to ensure a bright future for Northern Ireland workers and the thousands across the United Kingdom in the supply chain".
"Today's decision is a victory for innovation, competition and rule of law", Bombardier said in a statement released shortly after the vote. And it is planning to build the C-Series jets in a new plant in Alabama, creating hundreds of jobs.
"There's absolutely no reason now for the C Series to be built in Mobile, Alabama", he argued, adding that half the C Series-related jobs are already in the U.S.
"With this matter behind us, we are moving full speed ahead with finalizing our partnership with Airbus", the statement reads.
"Workers at Bombardier will be delighted tonight - they and the company are wholly vindicated by the ITC decision".
The two aircraft manufacturers made their closing arguments in separate submissions that painted dramatically opposing pictures. "Bombardier and its innovative workforce play a vital role in the Northern Ireland economy", she said.
Bombardier surged 16 percent to C$3.56 at 2:50 p.m.in Toronto after climbing as much as 23 percent for the biggest intraday gain in three months. "Period. And there may never be one", Boeing's lawyers argued in the company's most recent official filing with the commission.