In October 2016, TRICARE implemented full parity for mental health benefits to eliminate gaps between mental health and medical care benefits. This study examined the extent to which the implementation of mental health parity led to an increase in specialty mental health care use among TRICARE beneficiaries. We analyzed data came from the 2010-2020 Medical Expenditure Panel Survey, which collects the most comprehensive health and healthcare utilization data on the nationally-representative non-institutionalized U.S. population. The sample included adults aged 18-64 (5,138 TRICARE beneficiaries and 305,065 privately-insured/uninsured individuals) and children aged 5 to 17 (1,248 TRICARE and 70,676 privately-insured/uninsured children). Primary outcomes included psychotherapy visits and psychiatry visits, separately for office-based and hospital outpatient care settings. We employed novel statistical modeling techniques including event study difference-in-differences and propensity score matching to compare pre-post changes in the outcomes for TRICARE beneficiaries with counterfactual trends from the comparison group of non-TRICARE individuals. We estimated two-part count data models where probit and negative binomial are used for the first and second parts, respectively. We computed average marginal effects and bootstrapped standard errors. All estimates were survey-weighted and adjusted for a complex survey design. Our findings show that TRICARE’s mental health parity implementation had no statistically discernable effect on the probability of psychiatry or psychotherapy visit, for either adults or children. However, it led to an 8.9 (95% CI 1.9-15.9) visit increase in psychotherapy each year for adults who ever had a psychotherapy visit that year, mainly through office-based providers. The parity implementation led to an increase of 7.3 (95% CI 4.6-10.0) outpatient psychiatrist visits a year among children who ever had a visit. The increase in psychotherapy visits among adults was the largest for individuals with poor to low household income (17 more visits/year among those who had any visit). In comparison, the increase in psychiatrist visits among adults was the largest for those with high household income (4 more visits/year among those who had any visit). Mental health parity implemented in TRICARE overall led to an increased use of specialty mental health care services. However, the magnitude of the relationship varied by age group, care setting, and household income level. In conclusion, our analysis provides support for beneficial impacts of continued efforts to expand mental health benefits and coverage for TRICARE beneficiaries. Whether an increase in access to mental healthcare services translates into improved behavioral health conditions among TRICARE beneficiaries and other subsequent sequelae such as health readiness of Service Members warrant further investigation.