This paper presents the next-to-next-to-leading order (NNLO) QCD correction to the total cross-section for the process $ gg \rightarrow t\bar{t} + X $, completing the set of NNLO QCD corrections for top pair production at hadron colliders. The results are supplemented with soft-gluon resummation to next-to-next-to-leading logarithmic accuracy, leading to an estimated theoretical uncertainty of about 3% at the LHC and 2.2% at the Tevatron. The Standard Model predictions agree well with experimental measurements, demonstrating the high theoretical precision of this observable. The NNLO correction to the total inclusive cross-section for $ gg \rightarrow t\bar{t} + X $ is calculated and expressed in terms of functions $ F_{i} $, which include both analytic and fitted components. These functions are used to compute the cross-section, and the results are validated against known threshold behaviors. The calculation also includes the determination of the constant $ C_{gg}^{(2)} $, which is related to the hard matching coefficients needed for NNLL soft-gluon resummation. The NNLO+NNLL theoretical predictions for the top pair production cross-section at the Tevatron and LHC are presented, showing high precision with scale uncertainties of 2.2% at the Tevatron and 3% at the LHC. The predictions are compared with experimental data from the Tevatron and LHC, showing good agreement. The results are implemented in the program Top++ (v2.0), which includes scale and PDF uncertainties. The theoretical precision of the top pair production cross-section is very high, with the NNLO correction significantly reducing the scale dependence compared to NLO calculations. The predicted cross-section agrees well with all available measurements, and the high precision is expected to enable new precision collider applications, including parton distribution functions and searches for new physics. The work is supported by various funding bodies and acknowledges contributions from collaborators.This paper presents the next-to-next-to-leading order (NNLO) QCD correction to the total cross-section for the process $ gg \rightarrow t\bar{t} + X $, completing the set of NNLO QCD corrections for top pair production at hadron colliders. The results are supplemented with soft-gluon resummation to next-to-next-to-leading logarithmic accuracy, leading to an estimated theoretical uncertainty of about 3% at the LHC and 2.2% at the Tevatron. The Standard Model predictions agree well with experimental measurements, demonstrating the high theoretical precision of this observable. The NNLO correction to the total inclusive cross-section for $ gg \rightarrow t\bar{t} + X $ is calculated and expressed in terms of functions $ F_{i} $, which include both analytic and fitted components. These functions are used to compute the cross-section, and the results are validated against known threshold behaviors. The calculation also includes the determination of the constant $ C_{gg}^{(2)} $, which is related to the hard matching coefficients needed for NNLL soft-gluon resummation. The NNLO+NNLL theoretical predictions for the top pair production cross-section at the Tevatron and LHC are presented, showing high precision with scale uncertainties of 2.2% at the Tevatron and 3% at the LHC. The predictions are compared with experimental data from the Tevatron and LHC, showing good agreement. The results are implemented in the program Top++ (v2.0), which includes scale and PDF uncertainties. The theoretical precision of the top pair production cross-section is very high, with the NNLO correction significantly reducing the scale dependence compared to NLO calculations. The predicted cross-section agrees well with all available measurements, and the high precision is expected to enable new precision collider applications, including parton distribution functions and searches for new physics. The work is supported by various funding bodies and acknowledges contributions from collaborators.