The Weir firm was founded by W. John Weir, II, Esq. as Weir & Associates, LLC in 2008. Mr. Weir, an experienced litigator who had over 12 years of trial experience at that point in his career, envisioned Weir & Associates, LLC as a locally based, full-service litigation boutique that could serve the residents of Mercer County and surrounding vicinages in all aspects of civil litigation. Weir & Associates was originally based out of the Straube Center in Pennington, New Jersey and initially specialized in civil defense litigation.

Robert Luthman, Esq. joined the firm as a partner in 2014 after 6 years of experience in civil litigation at a large central New Jersey firm. Now-partner Jeffrey Dunn, Esq., a lifelong resident of Mercer County, joined the firm as an associate in 2015 after having worked in recruiting prior to attending law school.

In 2018 the firm acquired the assets of Daly Law, LLC - a Ewing, New Jersey-based personal injury firm that was founded by the late Paul Daly, Esq. The firm adopted the professionalism and relentless advocacy for clients for which Mr. Daly was so well known and revered in Mercer County. In 2018 the firm also changed its name to Weir Attorneys. Weir Attorneys continued to operate out of Daly Law's location on Scotch Road in Ewing, New Jersey as well as out of the Straube Center in Pennington, New Jersey.

In 2019, Weir Attorneys combined the Scotch Road and Straube Center offices and relocated to one of its two current locations at 2109 Pennington Road in Ewing, NJ.

In January 2023, the firm acquired Joseph D. Kaplan & Son - one of the oldest Trenton-based personal injury firms that was founded in 1917. The acquisition of the Kaplan firm brought with it Weir Attorneys' first Trenton, New Jersey office location.

In May 2023, Weir Attorneys added experienced trial attorney Scott L. Puro, Esq. and his support staff. Formerly a partner at the Backes & Hill law firm in Lawrenceville, New Jersey, Mr. Puro's practice areas include Workers' Compensation, Trusts & Estates, Estate Litigation, Wills, Commercial & Residential Real Estate Transactions, and Estate Administration. Mr. Puro and his staff operate out of the Trenton office.