Companies are now able to search and analyse up to two years of Twitter updates for market research purposes.
Firms can search tweets back to January 2010 in order to plan marketing campaigns, target influential users or even try to predict certain events.
Until today, only the previous 30 days of tweets were available for companies to search. Regular users can access posts from the past seven days.
UK-based Datasift is the first company to offer the archive.
Its existing customers will be able to use access "historical" tweets from today, the company said.
"No-one's ever done this before," Tim Barker, Datasift's marketing manager, told the BBC.
"It's a brand new service that we're bringing online - it's a massive technology challenge because of the amount of data that is pumped out every single day."
He said the company takes in roughly 250 million tweets every 24 hours, all of which are analysed for content - such as whether they were said in a positive or negative tone.
The software will also log location data and social media influence based in part on existing influence monitoring service Klout.
Private accounts and tweets that have been deleted will not be indexed by the site.
Datasift said they have seen a lot of demand for the product - with almost 1,000 companies joining a waiting list to access the service.
Twitter, which has been steadily building various revenue streams, will earn money from Datasift as part of a licensing fee.
The cost to businesses will depend on the company's size, with Datasift's entry-level package costing £635 ($1,000) per month for "individuals or developers".
The move has ignited concerns among privacy campaigners.
"People have historically used Twitter to communicate with friends and networks in the belief that their tweets will quickly disappear into the ether," argued Gus Hosein, executive director of Privacy International.
"The fact that two years' worth of tweets can now be mined for information and the resulting 'insights' sold to businesses is a radical shift in the wrong direction.
"Twitter has turned a social network that was meant to promote real-time global conversation into a vast market-research enterprise with unwilling, unpaid participants."
Meanwhile, online rights group the Electronic Frontier Foundation described the service as "creepy".
However, Mr Barker defended the technology, arguing that people using Twitter do so due to its public nature.
"The thing with Twitter that it was always created to be a public social network - which isn't the case with Facebook which is more of a blended model. Twitter has been public from day one.
"I don't see that this creates any new dilemmas because this information is being pushed out socially right now.
"What Datasift will do is help companies get a longer view of this and a better insight."
Access to the archive has been billed as a way for companies to harness discussion online to predict future events such as mass protests - as seen during the Arab Spring - or the rise and fall of stock prices.
However Ben Page, chief executive of research firm Ipsos-Mori, told the BBC he believed the real marketing power of Twitter lies not with "historical" material, but with real-time search.
"I think the archive is in some ways less interesting. It's great that it's there, and people will look at it, but I don't think it's game-changing."
But Mr Page added that any tool that claims to offer an insight into the often complex world of consumer behaviour will be welcomed by businesses.
"It will help the [businesses] who are trying to deal with consumers via social media target their activities a bit more.
"Whether they admit it or not, companies will use that."