"If the committee is going to do its job for Parliament, we need access to both government officials but also New Zealand's most published author on the subject," Smith told the Herald.
He said the Labour MPs' reasons for blocking Brady's appearance were "disingenuous".
"They said 'we should only hear from government officials' when Parliament needs to be able to hear from a wide range of expert views to be able to complete its inquiry successfully," he said.
Submissions closed in September but that was before the committee and Justice Minister Andrew Little decided that the issue of foreign interference was going to be the focus of the inquiry.
Brady said in a statement that the coalition Government had made it clear in two public strategy documents, as well as classified briefing papers made public, that it was very concerned about foreign interference activities in New Zealand and wanted address them.
The Attorney-General also asked the committee to discuss foreign interference activities.
"New Zealand needs to pull together as a country to face this problem, and we need a bipartisan approach to solving it.
"The Government must pass new legislation which will address foreign interference in our political system, and it needs to talk directly about the problem to the public, so they can make informed choices and understand what the concerns are," she said.
Justice committee chairman Labour MP Raymond Huo said the decision to decline Brady's late request was purely procedural.
The closing date for submissions was over five months ago on 23 September 2018 and the date was widely publicised by committee staff in the usual way, he said in a statement.
The Committee had asked the Security Intelligence Service, the Government Communications and Security Bureau and the National Assessments Bureau to appear.
"As committee chair, I am satisfied that the correct procedure has been followed and that the agencies will keep the committee well informed about any issues of foreign interference that may arise," Huo said in a statement.
The inquiry into the election is a regular inquiry held after every general election and the local body elections and focuses on a different theme each time.
Little wrote to Huo in October asking that the committee look at the resilience of the New Zealand electoral system against foreign interference risks, provide recommendations for improvement and reassure the public that they could vote in elections with confidence.
"Foreign interference in democratic elections is, and will continue to be, a matter of pressing concern ... It is vital that New Zealand's electoral system is protected against illegitimate interference by foreign states," Little wrote in his letter.
The decision comes against the backdrop of rising concerns about foreign meddling in elections around the world, with an ongoing investigation into Russian meddling in the US election and claims of Chinese interference in Australian politics.
New Zealand's relationship with China is a sensitive subject for the Government at present, exacerbated by the GCSB's decision to ban Chinese telecoms giant Huawei from Spark's 5G network rollout.
