Jeremy Corbyn hailed the Oldham by-election win as a "vote of confidence in our party" after Jim McMahon swept to victory for Labour.
McMahon secured a majority of more than 10,000 and an increased share of the vote in the by-election which was sparked by the death of long-standing MP Michael Meacher.
But Ukip leader Nigel Farage complained of a "bent" contest and said the party would file a formal complaint.
Labour leader Jeremy Corbyn's visit to congratulate Jim McMahon on his by-election victory in Oldham lasted less than five minutes.
Standing among a crowd of Labour supporters who had waited patiently in the cold for his arrival, Mr Corbyn made a brief speech praising Mr McMahon before leaving by car.
The party leader refused to answer any questions from the media during the short photo opportunity but hugged Mr McMahon, who said he was "overwhelmed" by his victory.
In his speech, Mr Corbyn said the victory showed how "strong" the Labour party is.
Jeremy Corbyn hailed the Oldham by-election win as a "vote of confidence in our party" as Jim McMahon held the seat for Labour.
A by-election in the historically safe Labour seat of Oldham would, ordinarily, be a foregone conclusion. These are far from ordinary times.
The Oldham West and Royton byelection will be a fascinating crash test - as Corbyn's Labour comes up against Ukip's northern force.