Broadly neutralizing antibodies (bNAbs) against HIV-1 envelope (Env) inform vaccine design and are potential therapeutic agents. We identified SF12 and related bNAbs with up to 62% neutralization breadth from an HIV-infected donor. SF12 recognized a glycan-dominated epitope on Env's silent face and was potent against clade AE viruses， which are poorly covered by V3-glycan bNAbs. A?3.3? cryo-EM structure of a SF12-Env trimer complex showed additional contacts to Env protein residues by SF12 compared with VRC-PG05， the only other known donor-derived silentface antibody， explaining SF12's increased neutralization?breadth， potency， and resistance to Env mutation routes. Asymmetric binding of SF12 was associated with distinct N-glycan conformations across Env protomers， demonstrating intra-Env glycan heterogeneity. Administrating SF12 to HIV-1-infected humanized mice suppressed viremia and selected for viruses lacking the N448 glycan. Effective bNAbs can therefore be raised against HIV-1 Env's silent face， suggesting their potential for HIV-1 prevention， therapy， and vaccine development.