[16] The Kansas City Royals selected Singer with the 18th overall pick in the 2018 Major League Baseball draft.

Singer was activated onto the Royals roster at the beginning of the 2020 season and made his Major League debut on July 25, 2020, against the Cleveland Indians, and pitched five innings of two-run ball in a no-decision.

With the 2020 Kansas City Royals, Singer appeared in 12 games, compiling a 4–5 record with 4.06 ERA and 61 strikeouts in 64+1⁄3 innings pitched.

[24] Singer started 29 contests for Kansas City during the 2023 campaign, registering an 8–11 record and 5.52 ERA with 133 strikeouts over 159+2⁄3 innings of work.

[25] Singer made 32 starts for the Royals in 2024, compiling a 9–13 record and 3.71 ERA with 170 strikeouts across 179+2⁄3 innings pitched.

[26] On November 22, 2024, the Royals traded Singer to the Cincinnati Reds in exchange for Jonathan India and Joey Wiemer.

[27] For Christmas 2018, Singer surprised his parents with a special gift by paying off a loan they had from the bank along with all of their debt.