Taoiseach Micheal Martin said moving to Level Five would have been an "enormous shock" to Irish people's lives.
Government officials last night rejected advice from NPHET to move to Level Five of the Living with Covid roadmap.
Instead, the entire country will now be placed on Level Three from midnight.
And today the Fianna Fail leader explained that moving to a full lockdown would have had serious consequences.
He told the Dail: "To move on Sunday to Level Five would have been an enormous shock to people and to jobs. Government has to take wider issues into consideration.
"You're looking at hundreds of thousands of people being made unemployed once you go to level five.
"So, it's not unreasonable for Government to take stock before deciding to go to that level in one fell swoop, knowing the implications it would have on economic stability."
He added: "It's not something I recommended to Cabinet lightly. The impact of moving to Level Five would have been very, very severe on the lives on many, many people.
"We know from our analysis of the pandemic to date that lockdowns affect lower paid people more, lower income groups more, the marginalised more.
"When schools close down it's disadvantaged students that miss out."
Meanwhile Chief Medical Officer Dr Tony Holohan has also given his latest update as he called for a "broad societal effort" to tackle Covid-19.
He said: "It is essential that there is a broad societal effort over the coming weeks. Every one of us has the power to interrupt the spread of this virus and now is a vital time to use it.
“Focus on what you can do; wash your hands regularly, wear a face covering, keep your distance from others, avoid crowds, limit your social network, know the symptoms and what to do if you experience them or are a close contact of a confirmed case.”
