"[1] The theme of Currents is personal transition, and "Let It Happen" was sequenced as the album's opening song to exemplify acceptance.

He intended to write lyrics for the section, which he dubbed the "speaking in tongues version", but found that it lacked the "groove" of its original incarnation.

[10] A remix of the song by electronic rock group Soulwax premiered on Zane Lowe's Beats 1 show on 8 September 2015.

The official music video for the song, lasting four minutes and seventeen seconds, was uploaded on 17 August 2015 to the group's Vevo channel on YouTube.

Pitchfork reviewer Ian Cohen awarded it the site's "Best New Track" designation, writing that the song "seems to be editing itself in real time with all manner of filters, manipulated vocals, swirling ambience, and a startling midsection where he mashes down the looper button and holds it.

"[19] Pitchfork placed the song fifth on its year-end list, calling it a "highly intimate, interior experience" that "isn't so much psych rock as psyche rock—the sort of insta-jam that feels like it's being broadcast to you via telepathy rather than a stadium PA."[21] Spin ranked the song seventh on the magazine's list of the year's best songs, calling it "the Discovery of psych-rock, eight minutes of steady vamping that coalesce into an ideal synthesis of Tame Impala's gentle, kaleidoscopic powers and big-tent EDM's ability to physically command.

[23] Time ranked it seventh-best as well, describing it as "mov[ing] through all the states of matter: lava-lamp keyboards give way to gaseous soundscapes, robot voices depose into fuzzy guitar riffs, and stuttering sound effects briefly make you think your speakers are having a meltdown.

"[24] Paste placed it ninth on their year-end song rankings, calling it the album's "thesis statement" and saying, "The song's multiple movements swell and bloom into the cosmic psych-rock that Tame Impala so cleverly wielded on Innerspeaker and Lonerism, but there's a new dimension added this time around".

[25] Popmatters ranked it eleventh-best of the year, calling it "both the album's overture and its thematic peak" while praising it for "hit[ting] a pinnacle for a contemporary indie pop more indebted to classic disco records than Pavement or the Pixies".

[27] The Village Voice named "Let It Happen" the 14th-best single released in 2015 on their annual year-end critics' poll, Pazz & Jop.

[28] Noisey named the song the 25th-best of the year, calling it "a near eight-minute tortured wail—as defiant as it is fearful" and "a remarkable, hallucinatory exercise as comfortable in a sprawling cosmic DJ set as it is a dorm room bong sesh.

Pitchfork ranked it the 47th-best song of the 2010s, with contributor Noah Yoo commenting, "with this heavy slab of space disco, Parker decidedly broke free of any preconceived notions about his abilities".

[34] In September 2018, an edited version of the song appeared in a Ford Motor Company television advertisement for their 2019 car lineup.