Andrew Jackson Jennings was born in Fall River in 1849 to Andrew M. and Olive (Chace) Jennings.

He had been Mr. Borden's lawyer for many years prior to the murders and continued his position by representing Lizzie.

After Lizzie's arrest on August 11th, Jennings sought the help of Colonel Melvin O. Adams, former assistant district attorney for Suffolk County of Massachusetts. Adams was active during the preliminary hearing between August 25th and September 1st 1892. By the start of the trial on June 5th 1893, Jennings had found help in George D. Robinson, the former Governor of Massachusetts.

Andrew Jennings gave the opening statement at Lizzie's trial on June 10th 1893. Instead of trying to outline the defense argument, he made a strong emotional plea by expressing his own personal regard for the Borden family, including the accused by detailing Lizzie's close relationship with her father. He also stressed Lizzie's church, charitable and volunteer efforts. His opening statement took 38 minutes.