Modi, who arrived here today, held wide ranging talks with his counterpart Antonio Costa.
He also addressed the Indian community and presented the Overseas Citizen of India card to Costa.
Deviating from protocol, Costa came to see off Modi.
"Concluding a historic visit to Portugal. Deviating from Protocol, PM @antoniocostapm see off PM @narendramodi, a warm goodbye," Ministry of External Affairs Spokesperson Gopal Baglay tweeted.
"PM @narendramodi visit takes #IndiaPortugal bilateral relations to new heights," Baglay said.
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Ahead of his US visit, Modi said he looked forward to the opportunity of having an in-depth exchange of views.
"My USA visit is aimed at deepening ties between our nations. Strong India-USA ties benefit our nations & the world," he had tweeted.
In a statement posted on Facebook, Modi said his two-day visit to Washington was at the invitation of Trump.
Apart from official meetings with Trump and his cabinet colleagues, Modi will be meeting some prominent American CEOs.