Over the last two decades, the European Parliament (EP) has been empowered to make European Union (EU) legislation more inclusive, transparent and accountable. Yet, co-legislation has increased informalization and seclusion, as an ever-larger proportion of legislative acts is pre-agreed between Parliament and Council prior to first reading. This article asks under which conditions informalization is democratically problematic or tenable. So far, 'early agreements' have been criticized for their lack of transparency and accountability, their challenge to deliberation and inclusiveness, and their differential empowerment of 'relais actors'. Little attention has been paid, however, to the representation of the parliamentary principal in trilogues. This article draws on Jane Mansbridge's selection model of representation to fill the gap; it argues that representation with a strong 'selection core' and a weak 'sanction periphery' is, prudentially, best-suited for bicameral bargaining, and it introduces normative standards that make the selection model democratically tenable. A close analysis of codecision's current practices and institutions shows that these fall short of 'good deliberation at initial selection' and of 'narrative accountability'; 'ease of maintenance and de-selection' is approximated and 'transparency in rationale' is strengthened in the EP's 2012 Rules of Procedure. Future reform should, therefore, introduce two democratically crucial, yet hitherto neglected, measures: open deliberation about the appointment of rapporteurs; and reason-giving and justification (in addition to reporting back) by trilogue negotiators.