The Defamation Act is designed to give those publicly expressing opinions clearer and better protection than previous libel laws.
The government said the changes will reverse the “chilling effect on freedom of expression current libel law has allowed”, and allow legitimate debate.
Critics believed that old libel laws failed to protect freedom of expression and open and honest public debate. In the past, scientists and academics claimed they faced unfair legal threats for fairly criticising a company, person or product.
Under the new law, which covers England and Wales, claimants must prove that any statements made against them have caused serious harm before action can be taken.
Justice minister Shailesh Vara said: “The introduction of these new measures will make it harder for wealthy people or companies to bully or silence those who may have fairly criticised them or their products.”
The move comes after four years of work by the Libel Reform Campaign, comprised of the organisations Sense about Science, Index on Censorship and English PEN.
Cases that sparked the campaign, which garnered considerable public backing, included that of science writer Simon Singh. He was sued by the British Chiropractic Association for saying they “happily promote bogus treatments” in a 2008 article, a case they later dropped.
Cardiologist Peter Wilmhurst also became a cause celebre having been sued by US company NMT Medical for questioning the safety of one of its heart devices at an academic conference.
Tracey Brown, director of Sense about Science, said that the Act was a “major step forward” in reforming libel laws. She added that protection for reviewed papers will help scientists and science publishers make decisions about what to publish based on truth rather than the fear of being sued.
Ms Brown added: “A lot will depend on how the courts apply the new law. We will keep it under review to see that the law does give scientists the increased confidence to publish that it promises.”
The new act provides qualified privilege to peer-reviewed material published in scientific and academic journals. According to analysis of the act by Sense about Science, this privilege will also extend to international conferences and court proceedings.
It also offers protection for those who publish material that is in the public interest, and stops repeated claims being made against a publisher over the same material.