The Trump Organization hired Brad Parscale in 2011 as a digital guru.
He was asked in 2015 to create a website for Mr Trump's exploratory White House bid and a year later became the campaign's digital director.
This is thought to be the earliest any incumbent US president has officially declared his re-election campaign.
There are 979 days to go until the 2020 election. President Barack Obama announced his re-election plans 582 days before his 2012 bid for a second term.
The president's son, Eric Trump, said in a press release on Tuesday: "Brad is an amazing talent and was pivotal to our success in 2016.
"He has our family's complete trust and is the perfect person to be at the helm of the campaign."
The president's son-in-law and senior adviser, Jared Kushner, said in a statement: "Brad was essential in bringing a disciplined technology and data-driven approach to how the 2016 campaign was run.
"His leadership and expertise will be help [sic] build a best-in-class campaign."
Mr Parscale, 42, of San Antonio, Texas, has been targeted by Democrats investigating alleged Russian meddling in the US election.
Mr Parscale said he had told lawmakers he had no knowledge of the alleged Kremlin plot to influence the campaign in favour of Mr Trump.
Last July, he tweeted: "I am unaware of any Russian involvement in the digital and data operations of the 2016 Trump presidential campaign."
Mr Parscale told a CBS 60 Minutes programme last year that his 100-strong digital team created up to 60,000 ads on Facebook to reach Trump supporters every day.
But he said Mr Trump had rebuked him because he was sceptical about digital ad spending.
Mr Parscale said Mr Trump shouted at him: "I don't believe in this mumbo-jumbo digital stuff."
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