The index came within a point of the historic level on January 6, as investors banked on pro-growth policies and tax cuts from the new administration.
But the venerable index had stalled recently, dropping modestly in consecutive weeks, as investors grew cautious as they looked for clarity on the administration's new policies.
"A seminal moment. It is just a number but it is a big number, it is certainly a flashy number," said Tim Ghriskey, chief investment officer of Solaris Group in Bedford Hills, New York.
"There is a real belief that Trump is real, he has been extremely active these first couple of days of the presidency and a change may happen faster than people had thought."
If the index remains above 20,000 by closing time, the 42-session surge from the first close above 19,000 would mark the second-shortest length of time between such milestones.
The 24 trading days between 10,000 and 11,000 from March 29 to May 3 of 1999 was the fastest.
The rise from 18,000 to 19,000 took the Dow 483 trading sessions.
The move since November 22, when the index closed above 19,000 for the first time, has been spearheaded by financial stocks - with Goldman Sachs and JPMorgan accounting for about 20 per cent of the gain.
The two banks have benefited as investors bet that Trump's expected fiscal stimulus will trigger inflation and stoke a rise in interest rates.
On Wednesday, Boeing rose 2.3 per cent after its earnings and Goldman Sachs was up 0.7 per cent, helping to push the index over the top.
At 9:33 am ET (1433 GMT), the Dow was up 97.59 points, or 0.49 per cent, at 20,010.3, the S&P 500 was up 10.33 points, or 0.45 per cent, at 2,290.4 and the Nasdaq Composite was up 38.17 points, or 0.68 per cent, at 5,639.13.
The S&P and the Nasdaq also hit record intraday highs.
Advancing issues outnumbered decliners on the NYSE by 1,883 to 736. On the Nasdaq, 1,706 issues rose and 500 fell.
The S&P 500 index showed 51 new 52-week highs and no new lows, while the Nasdaq recorded 96 new highs and five new lows.