Micheal Martin has praised Joe Biden's speech to the UN General Assembly and cited him as a key ally on tackling climate change and Covid-19.
The Taoiseach, speaking to reporters in New York, called Mr Biden a "committed multilateralist at heart".
On Tuesday, the US president used his first address before the UN General Assembly to declare that the world stands at an "inflection point in history" and must move quickly to act on the Covid-19 pandemic, climate change and human rights abuse.
Mr Martin praised Mr Biden, who has frequently cited his own love of Ireland and his own Irish ancestry.
The Taoiseach said that Mr Biden emphasised issues important to Ireland, such as climate change and the Covid-19 pandemic, as well as the importance of safeguarding democracy and freedom of expression.
The US president is scheduled to meet UK Prime Minister Boris Johnson at the White House.
Asked by reporters what message Mr Biden would have for the UK premier on Brexit, Mr Martin said: "He has been very consistent in terms of the messaging he has given Boris Johnson and the UK in relation to the implementation of the Northern Ireland Protocol."
The protocol was agreed by the UK and EU as a way to maintain a free-flowing land border on the island of Ireland after Brexit.
Unionists in Northern Ireland have been vehemently opposed to its terms, which see additional checks on goods arriving to the region from the rest of the UK.
On Tuesday, DUP leader Sir Jeffrey Donaldson wrote to the Speaker of the US House of Representatives, Nancy Pelosi.
In a letter, he said that the Northern Ireland Protocol had damaged Northern Ireland and was a threat to the Good Friday Agreement.
"The political, economic and constitutional difficulties created by the Protocol threaten prosperity in Northern Ireland and the quality of our status within the United Kingdom," he wrote.
Mr Martin told reporters that he was sure Mr Biden would say to Mr Johnson "that it is important to engage with the European Union".