As the term is typically used by members of a law department, can we define “primary law firm” (or variations such as “preferred counsel,” “key law firm”, “go-to firm,” “major law firm” and the like)? What makes a firm primary is typically the absolute amount paid to it during a year or over several years. The amount cut-off amount varies depending on the total spend of a law department so we should normalize the metric: a law firm is a primary law firm if it receives in a fiscal year more than 10 percent of the law department’s external spend.
A better definition would designate as a primary law firm one whose spend bulks that large over at least two years. With that longer time, the firm that works on a single large lawsuit or acquisition will less likely be deemed primary.
A different definition incorporates the idea that a firm that handles a very large portion of the work in a given practice area is a primary law firm. Listings of go-to firms by law departments come closer to primary law firms in this sense. Perhaps a cutoff should be that 50 percent or more of the spend in a fiscal year (or two years for the same reason explained above) for a practice area makes a firm a “primary law firm.”