  We implement electroweak renormalisation schemes involving the effective weak
mixing angle to NLO in Standard Model Effective Field Theory (SMEFT). After
developing the necessary theoretical machinery, we analyse a select set of
electroweak precision observables in such input schemes. An attractive feature
is that large corrections from top-quark loops appearing in other schemes are
absorbed into the definition of the effective weak mixing angle. On the other
hand, the renormalisation condition which achieves this involves a large number
of flavour-specific SMEFT couplings between the $Z$ boson and charged leptons,
motivating simple flavour assumptions such as minimal flavour violation for
practical applications. The results of this paper provide a valuable new
component for estimating systematic uncertainties in SMEFT fits by performing
analyses in multiple input schemes.
