Speaking at The Guardian's Changing Media Summit, Darroch said that NOW TV will complement the existing Sky Go subscription service and enable people to pay for just the content that they want, regardless of whether they are a Sky customer.
This means that they could opt to stream a new movie on a range of connected devices, or pay to watch a Premier league match without having to be a Sky Sports subscriber.
NOW TV, first announced back in January, is to launch later in the year with a range of content, starting with hundreds of films from Sky Movies, but later expanding to sport and entertainment.
Sky has said that it will be available to anyone in the UK on any connected devices, regardless of whether they take Sky Broadband.
It will act as an "additional choice for people who don't currently subscribe to a pay TV service" from Sky or Virgin Media, while also enabling Sky to further monetise its range of expensively-acquired content.
Darroch said that the web-TV service will have no minimum contract, as customers can choose from a variety of payment options, including monthly unlimited streaming of Sky Movies, or just specific pay-per-view access to certain titles.
Sky Go will remain a "bonus service" for existing Sky TV customers, offering access to live channels and on-demand content depending on their subscription.
In his speech, Darroch said that the launch of NOW TV alongside Sky's pay-TV service allows the firm to cover a broader range of customers.
"The launch of a second brand is an exciting opportunity for us and the rationale is very simple. Having two brands will allow us to meet the needs and preferences of different customer segments more effectively," he said in the opening keynote of the conference.
"We'll offer two distinctive ways to watch: the market-leading full Sky service for the whole family, complete with the widest range of channels, high quality products like Sky+, HD and Sky Go, and the peace of mind of a monthly bill; or the flexible, more spontaneous, pay-as-you-go service of NOW TV.
"Because NOW TV will also be 'powered by Sky', customers will still know that it will give them the best, exclusive content and a high-quality experience from a provider they can trust. Either way, we believe we can offer even more customers a product that's just right for them."
Darroch said that the launch of NOW TV is also part of Sky's mission to make it easier for customers to access its content across a range of platforms.
"As the quality of the TV experience over broadband has improved, people have become more willing to consume content in different ways," he said.
"That presents a great opportunity to distribute our programmes which wasn't there even a year or two ago. With the long-awaited explosion of connected devices now upon us, this opportunity is only going to grow. And it's something we believe is highly complementary to our existing service.
"Today, we know that around 13 million homes don't yet take pay-TV from any provider. So we can reach out to them and offer them another way to access and watch our content."
NOW TV will be available across a wide range of connected devices, including PCs, Macs, laptops, tablets, mobile phones, games consoles and connected TVs.
It will have an "intuitive interface" featuring recommendations and editorial support, although it is unclear whether this will feature Zeebox, the social TV service of which Sky owns a 10% stake.
More details about NOW TV will be revealed closer to the launch, said Darroch.