The provisions were brought into effect by a commencement order passed on Sunday.
The clarified rules on predetermination still require a planning committee member to have an open mind when determining a planning application. However, proof of previous campaigning against a proposed planning application would not be proof that the member had a closed mind.
The Localism Act is aimed at devolving power from central government to local authorities and communities. It received Royal Assent in November 2011 and the majority of its provisions are being brought into effect in stages, using commencement orders.
New planning enforcement rules have also been brought into effect, in advance of more substantive provisions that are expected to be brought into force in April 2012. The new rules give councils the ability to take action against people who deliberately conceal unauthorised development.
"Today is a major landmark in the Government's unrelenting drive to hand power back to where it belongs - in the hands of citizens, community groups and local councils," said Andrew Stunell, Communities Minister.
"The new rights and powers coming into force will begin to put communities firmly back in control...This marks another shift away from the central government monopoly over public policy," said Stunell.
The remaining provisions of the Localism Act are expected to be in place by April 2012.