Thyrotropin (TSH) activation of the TSH receptor (TSHR), a 7‐transmembrane‐spanning receptor (7TMR), may have osteoprotective properties by direct effects on bone. TSHR activation by TSH phosphorylates protein kinases AKT1, p38α, and ERK1/2 in some cells. We found TSH‐induced phosphorylation of these kinases in 2 cell lines engineered to express TSHRs, human embryonic kidney HEK‐TSHR cells and human osteoblastic U2OS‐TSHR cells. In U2OS‐TSHR cells, TSH up‐regulated pAKT1 (7.1±0.5‐fold), p38α (2.9±0.4‐fold), and pERK1/2 (3.1 ±0.2‐fold), whereas small molecule TSHR agonist C2 had no or little effect on pAKT1 (1.8±0.08‐fold), p38α (1.2±0.09‐fold), and pERK1/2 (1.6±0.19‐fold). Furthermore, TSH increased expression of osteoblast marker genes ALPL (8.2±4.6‐fold), RANKL (21±5.9‐fold), and osteopontin (OPN; 17±5.3‐fold), whereas C2 had little effect (ALPL , 1.7±0.5‐fold; RANKL , 1.3±0.6‐fold; and OPN , 2.2±0.7‐fold). β‐Arrestin‐1 and ‐2 can mediate activatory signals by 7TMRs. TSH stimulated translocation of β‐arrestin‐1 and ‐2 to TSHR, whereas C2 failed to translocate either β‐arrestin. Down‐regulation of β‐arrestin‐1 by siRNA inhibited TSH‐stimulated phosphorylation of ERK1/2, p38α, and AKT1, whereas down‐regulation of β‐arrestin‐2 increased phosphorylation of AKT1 in both cell types and of ERK1/2 in HEK‐TSHR cells. Knockdown of β‐arrestin‐1 inhibited TSH‐stimulated up‐regulation of mRNAs for OPN by 87 ± 1.7% and RANKL by 73 ± 2.4%, and OPN secretion by 74 ± 10%. We conclude that TSH enhances osteoblast differentiation in U2OS cells that is, in part, caused by activatory signals mediated by β‐arrestin‐1.—Boutin, A., Eliseeva, E., Gershengorn, M. C., Neumann, S. β‐Arrestin‐1 mediates thyrotropin‐enhanced osteoblast differentiation. FASEB J. 28, 3446–3455 (2014). www.fasebj.org