Green’s Dictionary of Slang

(orig. US) a lawyer, esp. an assiduous one.

1949		Gordon & Kanin Adam’s Rib 31: Why do you stay married to a legal beagle with ten thumbs?
1956		‘Toney Betts’ Across the Board 42: A venerable legal beagle from Brooklyn, Robert Elder.
1988		D. Poyer Med 323: What the hell did that mean? It sounded like some goddamn legal beagle had written it.
1990		L.C. Troyer Portage Pathways (1998) 99: The big-city legal beagle made a remark which clearly questioned Caris’s honesty.
2000		Guardian 14 Nov. 🌐 The most difficult thing is when it’s acrimonious and the legal beagles are involved. We often find as a school that parents want to use you as piggy-in-the-middle to gather evidence against the other parent.
2000		T. Fontana ‘A Town Without Pity’ Oz ser. 4 ep. 7 [TV script] While you were downstairs with your legal beagle I thought, shit, there’s a whole bunch of other names I can use [for you].
2021		J. Ellroy Widespread Panic 195: The mag hired ace legal beagles [...] I read legal briefs.