The move, which Ofcom has called 'virtual unbundling', is designed to ensure fibre-based broadband access will be available to everyone in the UK.
Under the watchdog's proposals, BT will also be required to allow other ISPs to access underground ducts and telegraph poles, along with sharing information regarding the capacity and quality of ducts and poles.
Research by Ofcom revealed that up to half of BT's underground ducts have space for new cables in some areas.
Ofcom also said BT will be allowed to set the prices the ISPs are charged for the access to enable a fair rate of return.
"Super-fast broadband is starting to be a reality in the UK, with very significant advances in recent months in the speeds some providers are offering," said Ofcom's chief executive, Ed Richards.
"Ofcom's proposed regulatory framework is intended to support the next phase of development by promoting investment, competition and innovation for consumers across the UK."
Mike Wilson, broadband manager at comparison site Moneysupermarket.com, said Ofcom's announcement was a step in the right direction "to ensure effective competition in the market and a fair deal for broadband users".
"Ofcom and the government overseeing the next generation roll-out must ensure this remains the case, particularly in rural areas where infrastructure and competition is limited."
However, BT said following talks with Ofcom its network was already open to other ISPs.
"BT's fibre network is already open to all Communication Providers. It has been since we started to deploy it at the start of this year," the ISP said.
"Ian Livingston [BT's CEO] said in 2008 that it would be open on a fair and equivalent wholesale basis and nothing has changed. We are not being 'forced' to provide access. That access already exists."
Ofcom's move comes just a day after Prime Minister Gordon Brown annouced he wanted every Brit to have "super-fast" broadband access by 2020.