Witney was the seat of former Prime Minister David Cameron, and the by-election took place after Mr Cameron announced his resignation as an MP in September.
In his acceptance speech, Mr Courts paid tribute to Mr Cameron as “a great Prime Minister and a brilliant MP” for the Oxfordshire constituency.
He said: “Now we are going to move forward to build a country that works for everyone, our society should work for everyone, our economy should work for everyone and our democracy should work for everyone”.
The CFI team campaigned in Witney last week in support of Mr Courts. Mr Courts is a barrister by profession and has been representing local residents as a West Oxfordshire District Councillor since 2014.
A by-election was also held yesterday in Batley and Spen, the seat of deceased MP Jo Cox. Mrs Cox was murdered in her constituency in June, by a man suspected to have neo-Nazi links.
Labour candidate Tracy Brabin won the seat with an 85% share of the vote in the seat, which was not contested by other major parties out of respect for Mrs Cox.