Boston Blue was not originally conceived as a Blue Bloods spin-off; it began as a pitch by writers Brandon Sonnier and Brandon Margolis for a drama titled after the Boston neighborhood Jamaica Plain, focused on a transfer from the LAPD to Boston.

Talk of a Blue Bloods 'franchise extension' first surfaced in June 2024 when Paramount Global co-CEO Brian Robbins mentioned the idea at a shareholder presentation, and CBS later ordered the series direct-to-series in February 2025, giving it a 20-episode order.

The character Lena Silver, played by Sonequa Martin-Green, was originally referred to in early announcements as Lena Peters, using her mother's maiden name.

Ernie Hudson, who joined as a series regular playing Reverend Edwin Peters, had previously guest-starred on Blue Bloods as a different character back in Season 8 in 2018.

Mika Amonsen was cast to play Sean Reagan, recasting the role previously portrayed by Andrew Terraciano on the original Blue Bloods series.

Tom Selleck, when asked about participating in a possible spin-off, said he was 'open to suggestions' because he loves the Frank Reagan character, but doubted the character would retire to a small town.

Most filming for the series takes place in Toronto for financial reasons amid broader challenges facing the U.S. filming industry.

Donnie Wahlberg pushed to film at least some scenes in Boston itself, and in August 2025 the production shot exteriors at Fenway Park and Boston Common as a compromise.