In August he visited the striking actress on set in Toronto, where they were spotted cycling, sparking rumours of a reconciliation.
But nothing was official until Thursday, when the pair had a night out with superstar friends Elton John and David Furnish.
Their blissful smiles combined with their cosy body language were sure signs that the romance is well and truly back on.
The couple seem to have worked through their problems.
At the time of their break up, friends and relatives said Justin wanted to concentrate on his career rather than settle down.
And the cracks began to show when Jessica threw a surprise 30th birthday party for Justin at the start of the year.
According to the Daily Mail, The Social Network actor appeared to be embarrassed and uncomfortable by an emotional speech his girlfriend made to toast his milestone year.
But by the summer he seemed to have had a change of heart. The charismatic performer gave a heartfelt interview to Vanity Fair in July, in which he opened up about just how much Jessica meant to him.
Refusing to go into details of the split, he said: "I have to protect things that are dear to me – for instance, her."
"She is the single-handedly most significant person in my life. In my 30 years, she is the most special person, OK? So I protect it ."
Let's hope it works out for the photogenic duo this time round.