In 2014 and 2015, Isaako played for the Cronulla-Sutherland Sharks' NYC team. In May 2016, he played for the Junior Kiwis playing at Five eighth against the Junior Kangaroos in their 34-20 loss at Piretek Stadium. In 2016, he joined the Brisbane Broncos. In May 2016, he played for the Junior Kiwis against the Junior Kangaroos for the second year in a row.
2017
In 2017, Isaako graduated to the Broncos Queensland Cup team, Souths Logan Magpies. During the season, Isaako would show great form for the Magpies and Broncos coach Wayne Bennett would eventually give him his NRL Debut in Round 19 against the Newcastle Knights, starting at fullback in the 34-22 win at Hunter Stadium. This was Isaako's only appearance for the Broncos for the 2017 NRL season but he would continue his great form in the Queensland Cup and would be named at Fullback in the Intrust Super Cup team of the season.
2018
After having a boom season in the Queensland Cup, Isaako would cement his spot in the Broncos backline, practically on the wing after the departure of Tautau Moga to the Newcastle Knights and injuries to high-profile recruit Jack Bird. In Round 1 against the St George Illawarra Dragons in the 2018 season opening match, Isaako would star for the Broncos even though they had game to forget after losing 34-12 at Jubilee Stadium. In Round 3 against the Wests Tigers, Isaako kicked a penalty goal in golden point extra time to give the Broncos a scrappy 9-7 win without scoring any tries, just with Isaako kicking 4 penalty goals and a field goal at Campbelltown Stadium. In Round 6 against the New Zealand Warriors, Isaako scored his first and second NRL tries in the Broncos 27-18 win at Mt Smart Stadium. In Round 11 against the Sydney Roosters, Isaako had a match to remember, scoring 2 tries and kicking 4 goals, 1 of tries coming from nothing after he was pressured from Roosters defenders after an attempt to kick a field goal, so he stepped around defenders in a razzle dazzle fashion and scored a magnificent try to win the match for the Broncos with 2 minutes in the 28-22 victory at Suncorp Stadium. On 24 June 2018, Isaako made his international debut for New Zealand against England in the historical test match set in Denver, USA, starting on the wing and kicking 3 goals in the 36-18 loss at Mile High Stadium. As Isaako would show excellent form for the Broncos, between Round's 19-21 Isaako started at fullback and incumbent fullback Darius Boyd would shift to centre, showing some success but would go back to the wing for the rest of season. On 19 July 2018, Isaako extended his contract with the Broncos to the end of the 2024 season, after rejecting a rich offer from the Sydney Roosters. Isaako finished his exciting 2018 NRL season with him playing in all of the Broncos 25 matches, scoring 11 tries and kicking 97 goals, being the club's highest point scorer with 239 points. On 26 September 2018, at the 2018 Dally M Awards, Isaako received the Rookie of the Year award and his magnificent match winning try against the Sydney Roosters in Round 11 was named as the Try of the Year. On 1 October 2018, Isaako was named in the New Zealand squad for their tour of Great Britain. Isaako would play in 1 match, which was the last of the 3 matches against England, playing on the wing in the 34-0 win at Elland Road in Leeds. On 26 October 2018, Isaako became a father after his partner Abby Sutherland give birth their newborn son Isaiah Jamayne Isaako.
2019
As Isaako struggled to hit the heights of last year with uncharacteristic errors creeping into his game as the Broncos struggled with a 2-6 start leading up to the Round 9 Magic Round match against the Manly-Warringah Sea Eagles, Isaako alongside James Roberts were dropped from the team for defensive and handling issues. Isaako only sat out for the match as the Broncos won 26-10 at Suncorp Stadium. Isaako returned to his wing spot the week later in Round 10 against the last year premiers the Sydney Roosters, kicking 3 goals in the much needed strong 15-10 win at Suncorp Stadium.
