OnePlus was founded on 16 December 2013 by former Oppo vice-president Pete Lau and Carl Pei. According to Chinese public records, OnePlus' only institutional shareholder is Oppo Electronics. Lau denied that OnePlus was a wholly-owned subsidiary of Oppo and stated that Oppo Electronics and not Oppo Mobile (the phone manufacturer) is a major investor of OnePlus and that they are "in talks with other investors." The company's main goal was to design a smartphone that would balance high-end quality with a lower price than other phones in its class, believing that users would "Never Settle" for the lower-quality devices produced by other companies. Lau explained that "we will never be different just for the sake of being different. Everything done has to improve the actual user experience in day-to-day use." He also showed aspirations of being the "Muji of the tech industry", emphasizing its focus on high-quality products with simplistic, user-friendly designs. Continuing Lau's association with the platform from the Oppo N1, OnePlus entered into an exclusive licensing agreement with Cyanogen Inc. to base its products' Android distribution upon a variant of the popular custom ROM CyanogenMod and use its trademarks outside of China.

On 9 March 2014, the company expanded its operations to the European Union.

In April 2014, OnePlus hired Han Han to help market its products in mainland China.

The company's first product was the highly anticipated OnePlus One. It was unveiled on 22 April 2014, and was claimed as the "2014 Flagship Killer." The One had comparable, and in some ways better, specifications to other flagship phones of the year, while being sold at a significantly lower price at $299 for the 16 GB version or $349 for the 64 GB version.

On 23 April 2014, OnePlus began its "Smash the Past" campaign. The promotion asked selected participants to destroy their phones on video in an effort to purchase the OnePlus One for $1 (US). Due to confusion, several videos were published by unselected users misinterpreting the promotion and destroying their phones before the promotion start date. OnePlus later revised the rules of their promotion by allowing consumers to donate their old phones. There were 140,000 entrants in the contest with 100 winners.

On 13 August 2014, OnePlus hosted a contest to give invites, which were hard to come by at the time, to their female forum members. Users were asked to post a photo of themselves with the OnePlus logo, images would be shared in the forum and could be "liked" by other forum members.

On 16 December 2014, The Supreme Court of India and Delhi High Court banned the import and sale of OnePlus One phones following a lawsuit by Micromax alleging it has exclusivity for shipping phones with Cyanogen OS software in India.

On 21 December 2014, the ban was lifted. The device continues to be shipped with Cyanogen OS; however, a customized version of Android specially designed by OnePlus and named OxygenOS has been released, allowing later OnePlus devices to be sold in India.

OnePlus made its products available in Southeast Asia for the first time, partnering with Lazada Indonesia on 23 January 2015 and was expected to expand during that year throughout the region.

The OnePlus 2 was the successor to the company's highly successful first phone. It was unveiled a little over a year after the One, on 27 July 2015. It was highly promoted as the "2016 Flagship killer". There were very high expectations for the second generation OnePlus phones, partly because the company managed to create a high amount of hype for the upcoming phone. One of the marketing channels used was YouTube tech reviewer MKBHD who was sent a unit, which he covered in detail leading up to the launch.

The OnePlus X was OnePlus' entrance to the budget phone market, at 5 inches instead of the One and 2's 5.5 inches. The phone was unveiled on 29 October 2015. The phone was sold for $249, and consisted mostly of the same internal components as the year and half old OnePlus One, but had an AMOLED display.

In June 2016, OnePlus decided to pull out of the Indonesian market due to local regulations for imported 4G smartphones restricting sales of the OnePlus 2.

Early phones were only available through a system whereby customers had to sign up for an invite to purchase the phone at irregular intervals. The system was claimed to be necessary for the young company to manage huge demand. OnePlus ended the invite system with the launch of OnePlus 3 on 14 June 2016. Announced via an interactive VR launch event, the OnePlus 3 initially went on sale within the VR app itself. OnePlus touted the event as the world's first VR shopping experience. The phone was made available for sale later that day in China, North America, and the European Union on the OnePlus website, and in India on Amazon India.

The OnePlus 5 was unveiled on 20 June 2017 as the successor to the OnePlus 3, skipping the number 4. It launched with a Qualcomm Snapdragon 835, a dual-lens camera setup, up to 8 GB RAM, and up to 128 GB of storage. It was released in two colors: Midnight Black and Slate Gray.

OnePlus 3 had a third limited edition color, Soft Gold was released on 7 August 2017. Another special edition color was launched on 20 September 2017, in collaboration with Castelbajac.

The OnePlus 6T was unveiled on 29 October 2018. It launched with a Qualcomm Snapdragon 845, a dual-lens camera setup, up to 8 GB RAM, and up to 256 GB of storage. It also features a larger 6.41" 19.5:9 Optic AMOLED display with in-display fingerprint sensor and launched on OxygenOS based on Android 9 Pie. The camera has a 'Nightscape' mode which uses a longer exposure time to capture better photos in poor lighting conditions.

OnePlus set a Guinness World Record title of "the most people unboxing a phone simultaneously" on the launch of OnePlus 6T.

On 6, November 2018, OnePlus announced the first collaboration with McLaren for the launch of the OnePlus 6T McLaren Edition with the slogan "Unlock The Speed".

On 19, December 2018, Marques Keith Brownlee Announced in his video "Phone awards 2018" that his favorite phone of the year was the OnePlus 6T

The OnePlus 7T was officially presented in New Delhi on September 26 of 2019 and was available to order on September 28, followed by the 7T Pro unveiled 2 weeks later. The OnePlus 7T is the successor to the 7 that was released 5 months prior for the European and Asian market, and to the 6T for the American market where the OnePlus 7 wasn't available for sale. It features a new form-factor compared to its predecessors, with a 20/9 aspect ratio instead of 19.5/9. This allowed for OnePlus to make the phone ever so slightly taller than the older 6T and 7 while keeping the same width. OnePlus also decided to include the 90Hz Fluid AMOLED display found on the previous OnePlus 7 Pro. While OnePlus did keep the resolution at 2400×1080 pixels, the screen was one of its primary selling points. While the OnePlus 7T is considered a significant upgrade compared to the 7, the 7T Pro is a very subtle upgrade over the 7 Pro. It features the same display, same body, same camera system; the main changes being faster charging, faster processor and a slightly quieter pop-up camera.

After the success of the Oneplus 6T McLaren Edition, OnePlus announced their second collaboration with McLaren introducing the OnePlus 7T Pro McLaren Edition.

On January 7, 2020, OnePlus unveiled the Concept One smartphone at CES 2020. The OnePlus Concept One uses electrochromic glass to “hide” the rear-facing camera setup. The glass of the phone uses organic particles to create changes in transparency so that the glass covering the camera lenses can instantly shift from opaque black to transparent, presenting a clean, unbroken surface when not in use. OnePlus calls it a manifest of its ‘burdenless’ design philosophy. This optimal solution is called ‘Electronic CMF.' The rest of the design is inspired by the McLaren 720S supercar, with Papaya Orange leather on the rear of this concept phone and a sliver of glass right down the center of the rear panel of the device.

The OnePlus 8 and OnePlus 8 Pro were unveiled on April 14, 2020, and released on April 21 in Europe and April 29 in the United States.