Forty-nine percent of registered voters in the Dec. 3-7 survey said they approve of the job Trump is doing as US president, a 1 percentage point dip since a poll conducted late November.
By contrast, 51 percent of respondents disapprove of Trump's job as commander in chief.
Eighty-five percent of Republican voters approve of Trump, a 2-point tick up from last poll.
Eighty-two percent of Democratic voters and 56 percent of independent voters disapprove of the job Trump is doing in the White House.
The RealClearPolitics average has Trump's job approval at 45 percent.
Trump has yet to concede the 2020 election to President-elect Joe Biden, citing baseless claims of widespread voter fraud.
The Supreme Court rejected Trump's emergency bid to overturn the election results, the most prominent blow yet to the president's post-election legal battles.
The Hill-HarrisX poll was conducted online among 3,785 registered voters. It has a margin of error of 1.58 percentage points.