Thawing of Ukraine crisis and upbeat economic data from China helped domestic markets, said traders.
After gaining 263.08 points in the previous session, the Sensex advanced 67.13 points, or 0.32 per cent, to end at 21,276.86, a fresh six-week high.
At this level, the index is just 100 points away from its record closing high of 20,376.56 on February 7.
ICICI Bank, whose shares jumped 2.7 per cent, alone contributed about 41 points to Sensex's 67.13-point rise.
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The 50-share NSE index Nifty crossed key 6,300 level by adding 30.70 poins, or 0.49 per cent, to end at 6,328.65.
"Strength in global markets and positive economic data from China has boosted market sentiment. Sentiment shall also be impacted pre-elections and market may continue to show volatility ahead of the main elections time," said Rakesh Goyal, Senior Vice President, Bonanza Portfolio.
Election Commission announced dates for the high-stakes Lok Sabha elections to be held between April 7 and May 12.
Overseas investors bought Indian shares worth Rs 185 crore yesterday, their eleventh straight day of buying, analysts said.
Sectorally, the BSE Realty sector index gained the most by rising 1.95 per cent, followed by Banking index (up 1.47 per cent), Capital Goods index (1.13 per cent) and Metal index (0.68 per cent).