At a distance of 8596 miles (13,834km), it will be the airline's second longest flight after the Los Angeles to Singapore route launched in 2017, a route set to be the world's longest at 17 hours and 55 minutes and at a flight distance of over 14,000km.

The current title of the world's longest flight belongs to Qatar Airways. At 14,535km, the 17-and-a-half-hour Doha-Auckland service is currently the world's longest flight in terms of flight time after it knocked Air India's 15,127km, 15-hour Delhi-San Francisco route off its perch.

United Airlines now operates more 'ultra-long haul' flights than any other US carrier.

The route will be serviced by the airline's Boeing 787-9 Dreamliners and will commence on January 18, 2018.

See also: What it's like to be in economy on the world's longest flight

It will be the only non-stop service between Australia and Houston. Qantas currently operates a non-stop route to Texas from Australia; the Dallas to Sydney route, which covers a distance of 13,804 km.

The United flight to Houston from Sydney will take 15 hours and 45 minutes, and Houston back to Sydney would take 17 hours and 30 minutes, making it one of the longest flights in the world.

United currently operates services to Sydney non-stop from its West Coast hubs in Los Angeles and San Francisco.

See also: Could you survive the world's longest non-stop flight?

"We are looking forward to visiting Sydney and welcoming our Australian visitors with open arms to Texas," said Houston Mayor Sylvester Turner.

Scott Kirby, president of United Airlines said: "This new route will serve more than 70 cities across North America making the one-stop service to Sydney faster and more convenient than ever before."

Passengers will be able to take advantage of United's Polaris business class seats, which includes 48 lie flat beds. The Dreamliner service also includes 63 Economy Plus seats, which offers additional legroom and increased personal space, and 141 Economy seats.

From Houston, United offers nearly 500 daily flights to more than 170 destinations around the world. Of particular interest to Australian travellers, Houston serves as United's gateway to Latin America, flying into 51 destinations across Latin America and the Caribbean non-stop.

The Houston hub has recently seen an injection of $US277 million ($A343), with roomier gate areas, the latest technology and chef-inspired dining experiences.

See also: Qantas plan non-stop flights to New York and London

See also: Tips on how to survive long-haul flights

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