The move by the world's No.2 mobile operator came as Deutsche Telekom announced a limited rollout of 5G services in its German home market, stealing a march on competitors.
Nick Jeffery, chief executive of Vodafone UK, said offering unlimited data plans to both consumer and business customers would revolutionise the mobile market.
"We will give customers all the data they need, when and where they want it," he said.
Jeffery said Vodafone had examined how consumers used their devices and how it managed its network, including the efficiencies offered by 5G technology, before deciding to switch to unlimited data plans.
"We thought it was the right role for Vodafone to get back to its roots as a great British tech innovator," he told reporters.
EE, which is owned by BT, launched the first British 5G commercial service on May 30. It is offering a range of contract and sim-only deals for the ultrafast service.
Vodafone is taking a different approach by offering unlimited downloads tiered according to speed, starting from 23 pounds ($28.90) a month for up to 2 Mbps, 26 pounds for up to 10 Mbps and 30 pounds for speeds as fast as the device and network will allow.
"Let battle commence, Vodafone is looking to go toe-to-toe with EE," industry analyst Paolo Pescatore said.
"The scale of its ambitions should not be underestimated. 5G represents a significant opportunity to turn around its fortunes in the UK."
He added that the 5G market would see a further boost when Apple releases its first 5G device, most likely next year.
HUAWEI UNCERTAINTY
Vodafone is launching the service with Xiaomi Mi Mix 3 and Samsung S10 5G handsets and a 5G router.
Both Vodafone UK and EE pulled 5G handsets made by China's Huawei from their launch line-ups because of uncertainty about support by Google's Android after a US move to block the Chinese firm's access to its technology.
The status of the ban remains unclear.
Jeffery said Vodafone always complied with government guidance on its products and services. "But if it's possible for us to sell a wider range of 5G devices, particularly the Huawei one, we will," he added.
Vodafone uses a range of telecom equipment suppliers including Huawei and Ericsson in its network, but it does not use the Chinese company in its core.
"Huawei is one third of our base stations, and the other two-thirds are other vendors," chief technology officer Scott Petty said.
"We like to use Huawei in base stations, they make great products and they work really, really well."
Britain was set to allow Huawei some participation in the radio part of 5G networks but bar it from the intelligent core.
But a decision has not been announced, and the US and some politicians are pushing for a more far-reaching ban.
Asked about the possibility of a total ban, Jeffery said Britain had to grasp the opportunity to be a technology leader. "Anything that slows us down is bad news for us all," he said.