CBCNews.ca will carry the prime minister's announcement live beginning at 12:30 p.m. ET.
Harper will be joined by International Development Minister Christian Paradis, who is also the MP for Mégantic-L'Érable, and Lac-Mégantic Mayor Colette Roy-Laroche.
Transport Minister Lisa Raitt announced on Wednesday that the federal government will now require railway companies to inform the communities their trains run through of the dangerous goods they are carrying.
Canadian Class 1 railway companies will have to report that information every three months while other companies will have to do so on an annual basis.
The train that derailed in Lac-Mégantic was carrying 72 tankers full of crude oil causing a series of explosions that killed 47 people and ripped the small community apart.
The timing of Harper's announcement in Lac-Mégantic will make it difficult for the prime minister to be back in Ottawa for question period at 2:30 p.m.
The Opposition New Democrats are expected to ask the Conservatives about the allegations contained in court documents filed by the RCMP about the Mike Duffy expenses scandal.
Harper's former chief of staff, Nigel Wright, and Duffy are alleged to have committed bribery, fraud on the government, and breach of trust between February and May 2013, according to the RCMP.