Exit polls suggest that black voters, particularly women, were decisive in the defeat of Alabama senate candidate Roy Moore.

The Republican, whose campaign has been mired in scandal following allegations he sexually assaulted teenage girls in his 30s, lost by 1.5 per cent of the vote to Democratic challenger Doug Moore.

Although black voters had not been expected to turnout at the special election, caused by the appointment of former Alabama Senator Jeff Sessions as Attorney General, polls indicate they may have made up between 28 and 30 per cent of the vote.

The African American community makes up 27 per cent of the Alabama population, according to the 2016 census.

Media coverage prior to the election suggested overall black participation would be lower than exit polls suggest it was.

According to a preliminary breakdown by the Washington Post, black women in particular made up a decisive component of the vote.

African American women made up 18 per cent of the vote and approximately 97 per cent of their vote went to Mr Jones – compared with 65 per cent of white women (who made up 30 per cent of voters) opting for Mr Moore.

In contrast, the vote among black men made up just 12 per cent of the vote even though 92 per cent voted for Mr Jones.

Mr Moore, a former conservative judge, is best known for defying a Alabama Supreme Court ruling ordering him to remove a monument to the Ten Commandments outside a judicial building in the state capital Montgomery.

He was also a prominent member of the birther movement which claimed Barack Obama was not born in the US, and has courted controversy for his comments about gay people and Muslims.

But his campaign was thrown into chaos by several women saying they had been sexually assaulted by him in the past – two of his alleged victims said they had been 14 and 16 respectively at the time.

Alabama Senate race: Roy Moore vs Doug Jones Show all 12 1 /12 Alabama Senate race: Roy Moore vs Doug Jones Alabama Senate race: Roy Moore vs Doug Jones Democratic senatorial candidate Doug Jones speaks to reporters after voting Getty Images Alabama Senate race: Roy Moore vs Doug Jones Republican Senatorial candidate Roy Moore (L) and his wife Kayla ride their horses to the polling station to vote AFP/Getty Images Alabama Senate race: Roy Moore vs Doug Jones David Watson waves in a Santa suit as he holds a Doug Jones sign AP Alabama Senate race: Roy Moore vs Doug Jones Republican Senatorial candidate Roy Moore speaks to the media as his wife Kayla (R) looks on AFP/Getty Images Alabama Senate race: Roy Moore vs Doug Jones Democratic Alabama Senate candidate Doug Jones casts his vote at Brookwood Baptist Church REUTERS Alabama Senate race: Roy Moore vs Doug Jones Roy Moore speaks to the media after he rode in on a horse to vote AP Alabama Senate race: Roy Moore vs Doug Jones Democratic candidate Doug Jones greets supporters after casting his ballot AP Alabama Senate race: Roy Moore vs Doug Jones Republican Senate candidate Roy Moore departs on horseback after he cast his ballot in Gallant REUTERS Alabama Senate race: Roy Moore vs Doug Jones Voters wait in line to cast their ballot at a polling station setup in the St Thomas Episcopal Church Getty Images Alabama Senate race: Roy Moore vs Doug Jones Democratic Senatorial candidate Doug Jones (L) greets voters outside of a polling station at the Bessemer Civic Center Getty Images Alabama Senate race: Roy Moore vs Doug Jones Voters exit after casting their ballots at a polling station setup in the Fire Department Getty Images Alabama Senate race: Roy Moore vs Doug Jones Democratic Alabama U.S. Senate candidate Doug Jones speaks with the media after casting his vote at Brookwood Baptist Church Reuters

It is also alleged he had ties to pro-Confederate groups who celebrate the anniversary of Alabama’s secession from the United States over slavery during the US Civil War, CNN reported.

Mr Moore’s defeat is an embarrassment for Mr Trump who campaigned hard for the former judge despite allegations about his private life.

The President was quick to congratulate Mr Jones on Twitter even though he attacked him during the campaign as a “Pelosi/Schumer Liberal Democrat” who would “always vote against what we must do for our Country” and is “bad on Crime, Life, Border, Vets, Guns & Military [sic]”.

Mr Jones' victory is seen as a breakthrough for the Democrats as it is the first time they have won a Senate race in the deeply conservative state since 1992.

The Democrats have been on the backfoot since the Republicans swept into power in the House of Representatives as well as many statehouses and governor’s mansions in 2010.