Rule II.8(a) of the Rules of the House of Representatives established OGC and the Bipartisan Legal Advisory Group. The rule is below in full:
Office of General Counsel
8. (a) There is established an Office of General Counsel for the purpose of providing legal assistance and representation to the House. Legal assistance and representation shall be provided without regard to political affiliation. The Speaker shall appoint and set the annual rate of pay for employees of the Office of General Counsel. The Office of General Counsel shall function pursuant to the direction of the Speaker, who shall consult with the Bipartisan Legal Advisory Group.
(b) There is established a Bipartisan Legal Advisory Group composed of the Speaker and the majority and minority leaderships. Unless otherwise provided by the House, the Bipartisan Legal Advisory Group speaks for, and articulates the institutional position of, the House in all litigation matters.
(c) The House, the Speaker, a committee or the chair of a committee authorized during a prior Congress to act in a litigation matter is authorized to act as the successor in interest to the House, the Speaker, such committee or the chair of such committee of a prior Congress, respectively, with respect to such litigation matter, and to take such steps as may be appropriate to ensure continuation of such litigation matter.
Source: Rules of the House of Representatives - 115th Congress (PDF)