The device retains a similar design to the HTC One (M7), its predecessor in the HTC One series, but features a larger, rounded chassis incorporating a 5-inch 1080p display, a quad-core Qualcomm Snapdragon 801 processor, a depth of field sensor which can be used to individually refocus and apply various effects to the foreground and background elements of photos taken with the device's camera, a higher resolution front camera, improvements to the device's front-facing stereo speakers, expandable storage, new gesture functionality, and a refreshed version of HTC's Sense software.

"[4] The device received mostly positive reviews, with particular praise devoted to the design improvements within its hardware and software, and its upgraded internals in comparison to the One (M7).

As was common during the early years of Android, HTC manufactured a large number of exclusive devices customized for several major U.S. carriers, who took on the role of marketing them.

[7][8] As a result, HTC planned to "leverage the momentum" and critical success of the One to produce an updated version for 2014, expanding upon concepts introduced by the previous model.

The company also planned to release a "much broader spectrum of products" in 2014, by placing an increased focus on the mid-range smartphone market with devices such as the Desire 816.

[10][11] In January 2014, Bloomberg News reported that the device would carry a similar design to the previous model, but with a larger screen of at least 5 inches in size, and that the phone would feature two cameras sensors to provide better focus, depth of field and image quality.

The first, by a Russian website on Twitter, revealed the rear of the device and confirming early reports about its design and dual-camera layout, with a dual-tone flash.

[13] Another leak by evleaks revealed an updated version of HTC Sense, retaining the BlinkFeed home screen, and depicting on-screen software buttons.

[14] In March 2014, a major leak occurred with the release of a 12-minute-long hands-on video by a YouTube user, detailing the device's HTC Sense 6.0 software and its inclusion of a microSD card slot.

Each video featured a highly technical explanation of a feature from the original One by an engineer, a simplified explanation by another person, followed by the engineer disclosing censored information about the new model[16][17] The new device, officially called HTC One (M8) or the new HTC One, was unveiled during a press conference on March 24, 2014, that was held simultaneously in London and New York City.

The previous design had been panned by critics for being irregular, and causing a black bar to occur on-screen if an app required the deprecated "Menu" key in violation of Android human interface guidelines.

[22][23][24] The hardware of the device was upgraded in comparison to its predecessor, using a 2.3 GHz quad-core Snapdragon 801 with 2 GB of RAM, and a 5.0-inch, 1080p Super LCD 3 touchscreen display with a pixel density of 441 ppi, protected by a layer of Gorilla Glass 3 with a scratch-resistance coating.

[30] HTC CEO Peter Chou said that the work on the Duo Camera took 18 months, in close collaboration with Qualcomm whose Snapdragon 801 ISPs were boosted to handle the device's imaging needs.

[31] While 2013 phone's (M7) rear camera had optical image stabilization (OIS), it was not included in the device as developers deemed it to be "incompatible" with the new depth sensor system.

[25] BlinkFeed was updated with a revised design, which only now displays the weather clock if it's set as the default home screen, and will also now allow third-party developers to add content sources through an SDK; Fitbit (whose app, also pre-loaded on the device, can integrate with its sensor hub as a pedometer) and Foursquare were announced as the launch partners for the SDK.

In October 2014, an update to 4.4.4 was released, adding a suite of enhanced camera features branded as "HTC Eye Experience"; this includes "Split Capture", "Photo Booth", and "Auto Selfie" modes, voice shutter, face tracking while recording video, and the "Live Makeup" filter.

[40][41][42] The Android 5 update introduces the issues of freezing, forced reboots, decrease in frame rates and lag when using the smartphone for heavy gaming.

In Germany the release was limited with only METRO-owned electronics store chains Media Markt and Saturn carrying the phone in small quantities.

Also, the radio supports less LTE-bands, most notably omitting band 20 which reduces LTE-usability in countries like Germany where providers prefer the 800 MHz frequency outside of downtown areas.

The device ships with several HTC-developed apps to provide Sense features on top of Windows Phone, such as ports of BlinkFeed, Sense TV, and Video Highlights, an HTC Camera app for using the Duo Camera and its depth mapping effects, and support for the Dot View Case and double-tapping the screen to wake it up.

TechRadar suggested that the HTC One (M8)'s design aged well against upcoming metal smartphones, being sufficient to "survive the onslaught of the iPhone 6 and the Galaxy S6".

[22][59][35] Some reviewers panned the increased height of the device and thick bezels compared to the preceding HTC One (M7) and other competing smartphones;[21] in particular Ars Technica criticized HTC for not using its shift towards software buttons to reduce the size of the device's bezel, noting that they did not remove the black strip below the screen where the previous, physical buttons were.

While it received praise for its low-light capabilities, faster autofocus, along with the updates to HTC's camera software, the camera was criticized for not showing any notable improvements in image quality over the previous model, producing soft-looking images that only looked acceptable at small sizes due to aggressive noise-reduction and inadequate software processing.