Trainor collaborated with producers such as Federico Vindver, Gian Stone, Grant Boutin, and Jason Evigan and featured artists included T-Pain, Lawrence, and Niecy Nash.

Its message centers on self-empowerment, women's empowerment, and positive self-talk, drawing inspiration from Trainor's family, motherhood, and her experiences in the music industry.

Trainor promoted Timeless with public appearances and televised performances on programs such as Today and The Tonight Show Starring Jimmy Fallon.

Meghan Trainor's popularity declined in the lead-up to the release of her third major-label studio album, Treat Myself (2020), and it received limited live promotion due to the COVID-19 lockdowns.

[10][11][12] Trainor hosted producer Gian Stone in an episode of her podcast Workin' on It in March 2023, during which she announced that she had one more album left in her contract with Epic Records.

Trainor wrote the song "Forget How to Love" with her brothers and Scott Hoying within 10 days after giving birth to her second son, who was born on July 1, 2023.

[18][34] She presents a feminist point of view on dating and emotional detachment in relationships, highlighting her concerns about the consequences of men's actions and societal misogyny while emphasizing women's empowerment.

[35] The opening track, "To the Moon", is a minor key 1960s-style torch song[32] which incorporates brass instrumentation, a compact groove, and club beats.

[18][17][34] "Been Like This", a collaboration with T-Pain, begins with a jazz-influenced intro and transitions into a trumpet melody,[26] combining hip-hop beats, synthesizers, and doo-wop with Charleston.

[36][37][38] "Crowded Room" is a doo-wop song that has the same "brassy sway" as Trainor's 2014 single "All About That Bass", but its harmonized vocals are distinct and "more quiet and intimate", according to DeWald.

[34][38] The fourth track, "Whoops", is a pop-doo-wop break-up song with influences of R&B, on which Trainor addresses an ex-partner and derides the woman who he cheated on her with.

[17][35] The ninth track, "Rollin'", has Brill Building production which incorporates strings, bass, and brass instrumentation; in its feminist lyrics influenced by her experiences in the music industry, Trainor addresses society's hypocritical expectations for women and the misogyny and mansplaining they endure from men, according to South China Morning Post's Rhea Saxena.

[32][34] The 11th track, "I Get It", is a pop song, followed by "Sleepin' on Me", which is a "return to that doo-wap/hip-pop hybrid style" according to Renowned for Sound's Graeme R.[14][38] "Hate It Here" has lyrics about disliking being at a club, which are playful and sarcastic according to critics.

[44][45][46] The second single, "To the Moon" was released on May 3, 2024,[47] followed by a music video which featured appearances by her son, Sabara, Nash, Olsen, and influencers Brookie and Jessie.

[50][51] Initially refraining from promoting any songs to radio stations unless they gained popularity on TikTok,[52] the label sent "Whoops" to them as the third single on June 24.

[55] Trainor sang "I Wanna Thank Me" during iHeartRadio's Can't Cancel Pride 2024, and "Been Like This" and "Whoops" at Capital's Summertime Ball 2024.

[34] AllMusic's Matt Collar thought Trainor borrowed a bit from all musical styles she had tried in the past, hitting several stylistic notes that popularized her, and delivered a "frothy, confident, mixtape of an album".

[32] Likewise, Graeme R found it a great addition to Trainor's discography and believed it focused on her musical niche despite her venturing into some other genres.

Collar believed that though doo-wop can be a whimsical and pastiche genre, the album was intelligently written and filled with melodic hooks that accentuate Trainor's talents as a pop songwriter as well as singer.

[34] South China Morning Post's Rhea Saxena praised Timeless and believed it would empower young women to resist sexism and toxic relationships.

[35] On the other hand, Jack opined that poor lyricism and incohesion kept the album's friendly focus below its aspirations and the repetitive theme of love created redundancy.