PSV Eindhoven Lammers joined
PSV Eindhoven's youth system in 2010, having previously played youth football for VOAB and
Willem II. He signed a three-year professional contract with PSV in July 2015. Lammers made his debut in professional football on 10 August 2015, when he faced
Go Ahead Eagles with
Jong PSV. On 8 August 2016, he scored a hat-trick in Jong PSV's 5–4 win against
Den Bosch. He was loaned out to
Heerenveen for the
2018–19 season.
Atalanta In September 2020, Lammers joined
Serie A club
Atalanta. The transfer fee paid to PSV was reported as €9 million plus €2 million in possible bonuses. On 4 October, he scored his first goal in a 5–2 win against
Cagliari. In September 2021, Lammers joined
Eintracht Frankfurt on loan for a season, without option to buy, to replace
André Silva who left Eintracht for
RB Leipzig. Lammers was an unused substitute in the
2022 UEFA Europa League final against future employer
Rangers. On 7 August 2022, Lammers joined Serie A club
Empoli on a season-long loan. In January 2023, this loan was terminated and Lammers joined
Sampdoria on loan until the end of the season.
Rangers On 15 June 2023, Lammers joined
Scottish Premiership side
Rangers for an undisclosed fee. He made his debut for the club on 5 August 2023, starting in a 1–0 defeat away to
Kilmarnock. He scored his first goal for Rangers during a league match at home to
Livingston on 12 August 2023. Lammers scored against Dundee in an away match in November 2023. On 10 January 2024, Lammers joined
Eredivisie club
Utrecht on loan until the end of the season. Lammers scored his first goal for Utrecht in a five nil win over Sittard. Following this Lammers went on an unprecedented run of form by scoring in seven consecutive matches for Utrecht which is a club record in the Eredivisie. During this goal scoring run this included a double in an away match against Heerenveen. Lammers finished his loan spell at Utrecht with further goals against Alkmaar and Rotterdam taking his total for the loan spell to eleven goals in twenty matches for the dutch side.
Twente On 26 July 2024, Lammers joined
Twente on a three-year contract. ==International career==