The most biographical element of A Tale of Two Cities is the version of innocent young love presented in Lucie Manette.
Dickens was a hopeless romantic, but his own life was not as romantic as he wanted. He married Catherine Hogarth, but he idolized her younger sister—who died very young. Lucy represents Mary Hogarth. She is the idealized, beautiful, young, innocent, and perfect flower.
Dickens describes how Lucie was able to hold her father together through tough times.
She was the golden thread that united him to a Past beyond his misery, and to a Present beyond his misery: and the sound of her voice, the light of her face, the touch of her hand, had a strong beneficial influence with him almost always. (book 2, ch 4)
Dickens is often accused of falling in love with Mary Hogarth after her death, while he was married to her sister. The truth is a little more complicated than that. Dickens longed for the perfect life, yet it eluded him. Because she died young and beautiful, he was not able to learn her faults. He therefore represented her in the idealized females in his books, especially Lucie Manette.