He graduated from Bowdoin College in the class of 1837, and came to Boston to study law in the office of Henry H. Fuller, whence in 1840, he was admitted to the bar.
During the earlier portions of his educational career, both in college and at the bar, he had no very brilliant successes. He had little ambition to dazzle or shine, or seek for immediate effect; he was indifferent to academic honors, his heart and mind being set upon higher things. He read and studied broadly and carefully, in reference to his whole manhood rather than to the exigencies of a passing occasion. Besides his legal studies, he was a widely read belles-lettres student, and his memory was most retentive of all sorts of literature, grave and gay, tragic and comic. He was one that took the journey of life in a leisurely way, stopping to admire prospects and to gather the flowers as he went on.
From the very earliest of his associations in Boston, he allied himself not only with popular and acceptable forms of philanthropy, but also with those which were under the ban of polite society. One who knew him well says: "Few men were connected with so many unpopular and unfashionable causes. Indeed, it was only sufficient to know that an alliance with any cause was considered to involve some loss of social caste, or business patronage, to be pretty sure that John A. Andrew was allied with it."
His cheerful, jovial spirit, and the joyousness with which he accepted the reproach of a cause, took from it the air of martyrdom. His exquisite flow of natural humor oiled and lubricated the play of his moral faculties, so that a gay laugh instead of an indignant denunciation would be the weapon with which he would meet injurious language or treatment heaped on him for conscience sake. Like Lincoln, he had the happy faculty of being able to laugh where crying did no good, and the laughter of some good men, we doubt not, is just as sacred in heavenly eyes as the tears of others. They who tried to put men under society's ban for their conscientious opinions, got loss on their own side in excluding Andrew, since no man had in a higher degree all the arts and faculties of agreeableness in society. No man had a wider or more varied flow of conversation. No man could tell a better story or sing a gayer song. No man was more gifted with that electrical power of animal cheerfulness, which excites others to gayety and mirth. In the intervals of the gravest cases, when pressed down, overwhelmed, and almost bewildered, he would still find spare hours when at the bedside of some desponding invalid, or in the cheerless chamber of old age, he would make all ring again with a flow of mimicry and wit and fun, as jolly as a bob-o-link on a clover head.