Around 27 per cent of people have now received their first vaccine dose, while 14 per cent have received both doses, making them fully vaccinated.
Taoiseach Micheál Martin paid tribute to vaccination teams across the country in advance of the target being hit.
He tweeted: “Just informed by @HSELive that we are likely to reach the total of 2 million #CovidVaccines given out across Ireland by the end of today.
“Another important milestone in our rollout – and tribute to the dedication of vaccines teams up and down the country.”
Health Minister Stephen Donnelly also praised the efforts of vaccinators in helping to reach the milestone.
Speaking from a vaccination center in Citywest on Thursday, he said: “It’s a huge amount of work.
“It just goes to show the amount of effort across the country, from all the different groups.
“There’s a lot of volunteers here as well, all over the campus, helping out.
“This truly is a national effort.
“I just want to say thank you to everyone involved.
“It’s likely that we will hit two million vaccine doses administered today.”
The vaccination program has been picking up pace, with a record 250,000 doses expected this week, rising to between 260,000 and 280,000 next week.
The largest single day was recorded on Thursday last week, when around 50,000 doses were given.
Of those vaccinated so far, 90 per cent of people aged 85 and over have received both doses along with 93 per cent of people aged 75 to 84.
Among those aged 65 to 74, 93 per cent have received their first dose, and 19 per cent have received their second dose.
And among those aged 55 to 64, 54 per cent have received their first dose, and six per cent have had their second.
In a submission to the National Immunization Advisory Council (Niac), the HSE have called for the Johnson and Johnson and AstraZeneca vaccines to be allowed “at least” for people aged 45-50.
New advice from Niac that will shape the future of the vaccine rollout is expected early next week.
It is considering whether to revise its recommendation that use of the J&J and AstraZeneca vaccines be limited to people over 50.
This has raised concerns that vaccines could go to waste, with the majority of over 50s expected to be vaccinated by the end of May, but large shipments of J&J due at the end of June.
The HSE have called for the age limits of those vaccines to be lowered.
HSE chief executive Paul Reid said the aim was to “keep the pace that we have, continue to do it safely and to utilize all of the vaccines throughout May and June”.
He added: “There’s no doubt that towards the end of June we have a high delivery volume of Janssen (J&J).
“So our submission was based on that, at least for the ages of 45 up to 50, we would be able to utilize the Janssen vaccine and likely, the AstraZeneca for those age groups.”
He said it would allow the rollout to continue based on age and would mean that up to 250,000 J&J doses are not wasted.