This systematic review and meta-analysis aimed to examine the effectiveness of psychological interventions for internalising disorders in youth when delivered in routine settings. Secondary aims were to examine the effectiveness of cognitive behavioural therapy and determine moderators of treatment response. The study was pre-registered (PROSPERO 2020 CRD42020202776). Databases were systematically searched (PsycINFO, Medline, Embase, PubMed, ERIC) in December 2022 and screened according to the PRISMA 2020 statement. Inclusion: School aged participants (4–18 years) with a primary internalising disorder; psychotherapy delivered in a routine setting (e.g. outpatient clinic, school) by setting staff; compared psychotherapy to any control in a randomised controlled trial; reported pre-to-post or pre-to-follow-up comparisons on the primary disorder according to child, parent or independent evaluator report; and was published in English. Risk of bias was assessed using the ROB 2.0 Cochrane tool. Results were synthesised using random effects to pool estimates. Risk ratios were used to analyse dichotomous data and standardised mean differences (SMD) for continuous data. Forty-five studies were included (N = 4901 participants; M = 13 years; range 8–16; SD = 2.5). Nine used waitlist control, 17 treatment as usual, 4 placebo; 15 compared psychotherapy to active control. Psychotherapy was associated with small significant effects pre- to post-treatment compared to non-active controls for anxiety (SMD = − 0.24 to 0.50) and depression (SMD = − 0.19 to 0.34) with effects differing by informant. Psychotherapy led to small significant pre-to-post-benefits in youth internalising disorders in routine settings. Results are limited by reporter type and follow-up.