he scored twice against BATE Borisov. McMillan goals secured a 3–1 aggregate win for Dundalk and guaranteed the club a place in the 2016–17 UEFA Europa League group stage. McMillan also became the League of Ireland's all-time leading scorer in the UEFA Champions League, overtaking Jason Byrne and Glen Crowe. After scoring two hat-tricks against Derry City and Longford Town in the 2016 Premier Division and scoring five goals in the UEFA Champions League, McMillan was named Premier Division Player of the Month for July 2016. McMillan was joint top-scorer in the 2016–17 UEFA Champions League qualifying phase and play-off round with five goals. While playing for Dundalk, McMillan has also been employed as an architect by O'Brien Finucane Architects, a company based in Dawson Street, Dublin. St Johnstone McMillan signed a contract running to the summer of 2020 with Scottish Premiership club St Johnstone in December 2017. He made his debut on 27 January 2018, as a substitute at home to Partick Thistle, however he only lasted 21 minutes before having to go off injured. The hamstring injury he sustained kept him out for nearly three months. On 5 May 2018, McMillan scored his first goal for St Johnstone, in a 5–1 win away at Motherwell. He moved on loan to Hamilton Academical in January 2019. On 4 September 2019, McMillan joined Falkirk on a season-long loan. McMillan left the Saints in July 2020. Return to Dundalk After two years in Scotland, McMillan signed again with Dundalk on 29 July 2020. He scored the winning goal against Inter Club d'Escaldes in the 2020 Europa 2nd qualifying round. Dundalk went on to qualify for the 2020–21 UEFA Europa League group stage and he scored two goals from the penalty spot in Dundalks 4-3 lost against Rapid Vienna at the Allianz Stadion. This equalled Glen Crowe's European record of 11 goals. On 6 December 2020, McMillan scored a hat-trick in the 2020 FAI Cup Final in a 4–2 win over Shamrock Rovers at the Aviva Stadium, becoming the third player ever to achieve the feat. He was part of the starting 11 as his side won the 2021 President's Cup, beating Shamrock Rovers on penalties after a 1–1 draw at Tallaght Stadium on 12 March 2021. He scored in both legs to help defeat Newtown A.F.C. and FCI Levadia Tallinn in the 2021–22 UEFA Europa Conference League qualifying phase and play-off