It will consider the treatment of thousands of people in the 1970s and 1980s who were given blood products infected with hepatitis viruses and HIV, and the impact this had on their families.
Sir Brian Langstaff, chairman of the inquiry, previously said the probe would examine whether there had been an attempt to cover up the scandal, and has promised a "thorough examination of the evidence".
Des Collins, of Collins Solicitors, which represents more than 800 victims, their families and eight campaign groups, said the inquiry which begins on Monday in London is critically important.
"For those affected, their families and the campaign groups this is a day few thought that they would ever see - and it is a testament to those who have campaigned so hard to make it a reality," he said.
"The feeling among our many clients is that they felt that the Government had washed its hands of them, but now those responsible - both in government and at pharmaceutical companies - will be held to account.
"For so many people whether affected or mourning those who have died owing to contaminated blood treatments, this is critically important."
He said the start of the probe will begin the long process of understanding how and why they received infected treatment from the NHS, the details of "the extensive cover-up that followed", and what the Government proposes to do about it.
Collins Solicitors said fewer than 250 of the haemophiliacs who were co-infected with both Hepatitis C and HIV remain alive, with most dying before 1997.
The firm said many of those who have survived face a lifetime of medication - having to cope with serious illness and discrimination.
According to the terms of reference, which were published in July, the long-awaited inquiry will consider "whether there have been attempts to conceal details of what happened" through the destruction of documents or withholding of information.
It will also consider if those attempts were deliberate and if "there has been a lack of openness or candour" in the response of the Government, NHS bodies and other officials to those affected.
Prime Minister Theresa May announced in July last year that an inquiry would be held into the events over the two decades, when thousands of haemophiliacs and other patients in the UK were given infected blood products.
The announcement was welcomed at the time by campaigners, who have been pressing for years for an inquiry into the import of the clotting agent Factor VIII from the US.
Much of the plasma used to make the product came from donors such as prison inmates, who sold blood which turned out to be infected.
The inquiry is expected to take at least two-and-a-half years, and will begin with a commemoration service and public opening statements as the three days of preliminary hearings start.