Every UK household will have to opt in if they want to be able to view online porn, David Cameron is expected to announce today.
Family-friendly filters which block pornography will be automatically selected for all new internet customers, it has been reported.
The Daily Mail said that all 19m UK homes with the internet will be contacted by service providers by the end of next year and ask whether family-friendly filters should be on or off.
Experts pointed out that filters have been around for many years, but many households choose not use them.
Cameron will also say that possessing violent pornography containing simulated rape scenes will be made a crime in England and Wales.
And he will set out plans for new laws so that videos streamed online in the UK are subject to the same restrictions as those sold in shops.
In an emotive speech he will warn that access to online pornography is "corroding childhood" as he demands tough action by internet giants to crack down on extreme content.
Experts from the Child Exploitation and Online Protection Centre (Ceop), which is set to become part of the National Crime Agency, will be given enhanced powers to examine secretive file-sharing networks, and a secure database of banned child porn images gathered by police across the country will be used to trace illegal content and the paedophiles viewing it.
The Prime Minister will acknowledge the issue of extreme and child pornography is "hard for our society to confront" and "difficult for politicians to talk about".
But, drawing on his feelings as a father, he will insist it needs to be addressed as a matter of urgency.
He will say: "I want to talk about the internet. The impact it is having on the innocence of our children. How online pornography is corroding childhood. And how, in the darkest corners of the internet, there are things going on that are a direct danger to our children, and that must be stamped out.
"I'm not making this speech because I want to moralise or scaremonger, but because I feel profoundly as a politician, and as a father, that the time for action has come. This is, quite simply, about how we protect our children and their innocence."
He will call for collective action on the agenda from Government, parents, internet and technology firms, schools and charities.
"I want Britain to be the best place to raise a family," he will say. "A place where your children are safe. Where there's a sense of right and wrong and boundaries between them. Where children are allowed to be children. All the actions we're taking come back to that."
In a move called for by women's groups, ministers will close a loophole which allows the possession of "rape" porn, bringing the position in England and Wales in line with that in Scotland.
Cameron will say: "There are certain types of pornography that can only be described as 'extreme'. I am talking particularly about pornography that is violent, and that depicts simulated rape.
"These images normalise sexual violence against women - and they are quite simply poisonous to the young people who see them."
He will add: "There are some examples of extreme pornography that are so bad that you can't even buy this material in a licensed sex shop. And today I can announce we will be legislating so that videos streamed online in the UK are subject to the same rules as those sold in shops.
"Put simply - what you can't get in a shop, you will no longer be able to get online."
Cameron will praise the work Ceop has already done to disrupt the so-called "hidden internet" where people share illegal files away from mainstream websites.
"Once Ceop becomes a part of the National Crime Agency, that will further increase their ability to investigate behind pay walls, to shine a light on the hidden internet and to drive prosecutions of those who are found to use it.
"So let me be clear to any offender who might think otherwise: there is no such thing as a 'safe' place on the internet to access child abuse material."
Cameron, who has faced criticism from Labour over cuts to Ceop's funding, will insist that the centre's experts and police will be given the powers needed to keep pace with technological changes on the internet.
He will also set out proposals to link the storage banks of illegal imagery held by police forces across the country to produce a single, secure database enabling officers from different areas to work together to "close the net on paedophiles".
The internet industry has agreed to use the database to proactively scan for, block and remove the images wherever they occur, he will add.
But he will give search engines including Google an October deadline to introduce further measures to block access to illegal content, claiming they have a "moral duty" to act.
Cameron will call for them to block any results for a blacklist of "abhorrent" search terms compiled by Ceop and will caution against any claim that it is beyond their technology.
He will also call for warning pages which pop up if people try to access illegal content to spell out more explicitly the consequences of their actions.
A Google spokesman said: "We have a zero tolerance attitude to child sexual abuse imagery. Whenever we discover it, we respond quickly to remove and report it."
Cameron's announcement was welcomed by women's groups and academics who had campaigned to close the "rape porn" loophole.
Fiona Elvines, of Rape Crisis South London, said: "The Government today has made a significant step forward in preventing rapists using rape pornography to legitimise and strategise their crimes and, more broadly, in challenging the eroticisation of violence against women and girls."