In posts on Facebook, Modi said he will be going to Ireland on September 23 - in the first visit by an Indian Prime Minister in almost 60 years - and hold talks with Taoiseach (Prime Minister) Enda Kenny.
"We hope to further develop strong people-to-people and economic ties with Ireland in the years to come. In Ireland, I will also interact with the Indian community," he wrote.
On September 24, Modi will travel to the US. "This visit seeks to build on the substantial ground covered during my last visit to USA and President (Barack) Obama's visit to India early this year."
Noting he was going to the US at "a historic moment when the United Nations is celebrating its 70th anniversary", he said that in July, he had written to 193 heads of governments outlining India's vision for UN agenda and reforms. "I am glad that leaders of several nations wrote back appreciating our vision."
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In New York City, Modi will address the UN Sustainable Development Summit for formal adoption of post-2015 new sustainable development agenda. "Coming from a culture that regards harmony as central to its ethos, I am glad to have an opportunity to address this forum. The new goals are closely aligned with India's vision for sustainable development and our flagship programmes for the same."
Revealing he will also participate in a summit hosted by President Obama on peacekeeping, he noted that India has been one of the largest contributors to UN peacekeeping forces, with over 180,000 troops - more than from any other country.
"We are proud of our peacekeeping forces spread across the world, ensuring peace in difficult circumstances. I will pay homage to all those brave men and women who sacrificed their lives for peace. And I look forward to sharing my thoughts on how to make peacekeeping more effective," he wrote.
Modi also said that India will host a summit of G-4 leaders in New York where the main agenda would be the UNSC reforms and the UN's 70th anniversary "is an appropriate moment for reform discussions to be accelerated" as the General Assembly has finally adopted a document that would form the basis of formal discussions on this matter.
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He said he will be meeting several world leaders and also hold interactions with leading investors and financial sector firms, including a working dinner where major Fortune-500 companies will be present to deliberate on investment opportunities in India. "We have been interacting with several American business leaders over the last year and the outcomes have been encouraging," he said.
He also said that he will be visiting the West Coast on September 26-27 and participate in several programmes. "It would be after a gap of almost 33 years that an Indian PM would be visiting the west coast - the home of start-ups, innovation and technology."
Modi said he will also be part of a Townhall Q&A at the Facebook HQ along with Mark Zuckerberg, and this was an event "you shouldn't miss".
"I have already invited you all to share your questions through Facebook or the 'Narendra Modi Mobile App.' I will also see some recent technological innovations at the Google (Alphabet) campus and Tesla Motors. I will address a Renewable Energy Roundtable with USDOC and Stanford University."
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He said he is also enthusiastic about the 'India-US Start-up Konnect'. "India is emerging as a hub of start-ups in a wide range of areas and we aspire to take this further. We want the world to see our innovation capabilities in the start-up sector. At this event, a group of Indian start-ups will showcase their innovations and forge partnerships with the vibrant American start-up industry. "
In San Jose, he will interact with the Indian community on September 27. "The Indian diaspora has left no stone unturned in strengthening India-USA ties. We are very proud of the accomplishments of our diaspora that has made immense contributions to both our societies," he said, adding hope his US visit will be fruitful and further deepen bilateral bonds.