The deal is a boost for Boeing at a time when the U.S. planemaker is battling industrial and financial constraints, and reflects upheaval in the jet market after Qatar Airways engaged in a contractual and safety dispute with Europe's Airbus SE (AIR.PA).
Boeing shares rose almost 5% after the freighter order was unexpectedly topped up by an order for the Boeing 737 MAX. The deal was timed to coincide with a visit to Washington by Qatar's emir in which the United States hailed the Gulf state as a major ally.
That followed days of frantic negotiations after Airbus revoked an order for 50 competing A321neo aircraft as part of a heated dispute with Qatar Airways over flaws in a larger jet.
Qatar Airways Chief Executive Akbar Al Baker said negotiators had "lost a lot of sleep" in the intervening two weeks and took a swipe at Airbus.
"We like to build long-term relationships with trusted partners where both parties work together towards a common purpose," he told a White House signing ceremony attended by leaders from Boeing and engine maker General Electric Co .
Airbus declined comment.
The provisional order for up to 50 of the 737-10, the largest member of the MAX family, makes Monday's deal a potential 100-plane package including options for later add-ons. Reuters reported the 737 MAX deal earlier on Monday.
The cargo part of the deal represents the first order for a freighter version of the world's largest twin-engine passenger plane, the 777X, whose entry to service has been pushed back by more than three years to late 2023 or beyond.
Boeing is banking on sales of the huge freighter to shore up its leadership of the cargo market and head off a recent challenge from Airbus, with a freighter version of its A350.
"(The 777X) will be an absolute world-beater," Boeing Chief Executive Dave Calhoun said at Monday's signing ceremony.
Boeing agreed to convert a third of Qatar's existing order for 60 777X passenger planes, for which there is currently less demand, to freighters in order to win the order.
Speaking on the sidelines of high-level meetings on energy security amid the Ukraine crisis, Al Baker trumpeted support for the U.S. economy from Qatar Airways, which has faced trade complaints from U.S. carriers over alleged subsidies.
"I am especially pleased that the aircraft order will further emphasise Qatar Airways' support for the U.S. economy and U.S. jobs," he said.
For Boeing, the deal marks a respite from a recent safety crisis over the MAX and delays with the 777X passenger jet and 787 Dreamliner, and a chance to win points for its own economic contribution after intense regulatory and political scrutiny.
Boeing said the freighter order would sustain more than 35,000 U.S. jobs with an annual economic impact of $2.6 billion.
Boeing has dominated air freight for years through its 767, 777 and 747 cargo jets, though it will be urgently pressing for more orders for the new freighter flagship.
About half of global cargo by value travels by air, and in turn half of that usually goes in the belly of passenger planes.
During the pandemic, many airlines have been forced to park unused passenger jets, driving up demand for cargo space on dedicated freighters at a time when e-commerce has been a lifeline for many during COVID-19 lockdowns.
But economists warn the trends could start to unravel as the pandemic eases.