The US-based agency upped India's rating to Baa2 from Baa3, changing outlook to 'stable' from 'positive', and said that reforms will help stabilise rising levels of debt.
Finance Minister Arun Jaitley termed the move as "belated recognition" of reforms undertaken by the government and said the reform agenda will continue with emphasis on higher spending on infrastructure and in rural areas.
Government officials expressed hope that other credit rating agencies such as S&P and Fitch would follow suit.
The one-level step-up from the lowest investment-grade ranking puts India in the league of the Philippines and Italy.
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India's sovereign credit rating was last upgraded in January 2004 to Baa3 (from Ba1). 'Baa3' was thelowest rating in the investment grade -- just a notch above the 'junk' status. Baa2 rating means investment grade with moderate credit risk, and is two notches above the junk grade.
The rating upgrade comes within weeks of the World Bank handing a 30-place jump to India on its ease of doing business ranking to place it at 100th rank.
"We welcome (the upgrade) and believe that it is a belated recognition of all the positive steps taken in India in the last few years which have contributed to the strengthening of the Indian economy," Jaitley said
It recognises major economic and institutional reforms undertaken by the government, he added.
He promised to stick to the path of fiscal discipline.
Railway Minister Piyush Goyal said the government will stay on the path of good governance and focus on effective delivery to people.
The government "is going to do what it has to do on the domestic front -- employment growth, economic growth, reviving investment," said Chief Economic Advisor Arvind Subramanian.
Economic Affairs Secretary Subhash Chandra Garg said the upgrade has recognised government efforts on fiscal deficit, consolidation and debt control.
Moody's said the upgrade is underpinned by expectation that "continued progress on economic and institutional reforms will, over time, enhance India's high growth potential and its large and stable financing base for government debt, and will likely contribute to a gradual decline in the general government debt burden".
Moody's projected India's real GDP growth to moderate to 6.7 per cent in the current financial year, from 7.1 per cent in 2016-17.
While GST and demonetisation have undermined growth over the near term, real GDP growth will rise to 7.5 per cent in 2018-19 as disruption fades, it said.
It went on to list demonetisation, Aadhaar system of biometric accounts and targeted delivery of benefits through the Direct Benefit Transfer (DBT) system intended to reduce informality in the economy as other measures that had an impact.
The government's efforts to reduce corruption, formalise economic activity and improve tax collection and administration, including through demonetisation and GST, both illustrate and should contribute to the further strengthening of India's institutions, it added.
However, challenges with implementation of GST, ongoing weakness of private sector investment, slow progress with resolution of banking sector asset quality issues and lack of progress with land and labour reforms at the national level remain, it said.
The rating could also face downward pressure if the health of the banking system deteriorates significantly or external vulnerability increases sharply.