The modified One M8 is being sold at roughly half the price of the same handset running Google's Android.
This is the first time the struggling manufacturer has released a Windows smartphone in more than two years.
One analyst said the new device was "almost certainly financially supported" by Microsoft, in an attempt to gain a foothold in the US market.
The new phone, which comes with Windows Phone 8.1 pre-installed, is available exclusively through US network provider Verizon.
When bought with a 24 month contract, it is priced at $99 (£60), approximately 50% cheaper than the Android One M8.
"Consumers love the HTC One M8 and today's introduction extends that enthusiasm to new audiences hungry for choice in their mobile experience," said Jason Mackenzie, president of HTC Americas.
He added: "Microsoft shares our vision, and that's why we committed to bringing the Windows Phone platform to the HTC One M8."
Android lossesThe Taiwanese firm, which originally made its name selling early versions of Windows phone handsets, has preferred Android devices in recent years.
However it has recently lost out to rivals such as Samsung, and while its flagship handset, the HTC One, received good reviews, these did not translate into strong sales.
In April, HTC posted losses of 1.88bn Taiwanese dollars (£37m; $63m) for the first three months of 2014, compared with a profit of T$85m a year earlier.
Shares in HTC have dropped by 38% in the past year.
Microsoft 'desperate'Daniel Gleeson, an analyst at the consultancy IHS Technology, told the BBC the move was a "big thing for Microsoft as they want a big push for Windows phones in North America".
"Microsoft are desperate for other manufacturers to develop Windows smartphones, and they almost certainly financially supported HTC to make this phone," he added.
"Microsoft needs to kickstart the whole Windows Phone ecosystem. Its apps do not get updated at the same frequency as Android or iOS equivalents."
As for the pricing of the phone, Mr Gleeson said, this was an attempt by HTC and Microsoft to position themselves as a cheaper alternative to the upcoming new iPhone.
Earlier on Tuesday, HTC's chief executive Peter Chou unveiled another new phone in Tokyo, aimed at the Japanese market.
The updated J Butterfly model, the HTL23, features a plastic body, but is otherwise similar to the Android One M8.
Source BBC - http://www.bbc.co.uk/news/technology-28856282
