In 1808, his brother Abbott entered his employ as chief clerk, and in 1814 became a partner in the firm, now called A.

The firm continued until Amos's death and became the greatest wholesale mercantile house in the United States.

It was successful even in the hard times of 1812 to 1815, and afterwards engaged particularly in selling woolen and cotton goods on commission.

In 1842, he decided not to allow his property to increase any further, and in the last eleven years of his life he spent in charity at least $525,000.

Among other things, Amos Lawrence donated libraries to academic institutions, established a children's hospital in Boston, and gave $10,000 for the completion of the Bunker Hill Monument (Lawrence's father had fought at the Battle of Bunker Hill).

He gave to many good causes on a smaller scale, taking especial delight in occasionally giving books from a bundle in his sleigh or carriage as he drove.

Samuel was in turn descended from John Lawrence of Wissett in Suffolk, England, who was one of the first settlers of Groton.

After Richards died in 1819, Amos Lawrence married Nancy Means Ellis, widow of former U.S. Representative for New Hampshire and New Hampshire Superior Court justice Caleb Ellis, on April 11, 1821.