Stephin Merritt has kept himself plenty busy the last 17 years.

The mordantly witty New York songwriter’s output has included four albums with the Magnetic Fields; one sound track, with the Gothic Archies, for Daniel Handler’s fiendish Lemony Snicket books A Series of Unfortunate Events; two albums with electro-pop outfit Future Bible Heroes; four solo LPs; and the musical Coraline, based on a Neil Gaiman children’s book.

But in that span, Merritt has never undertaken a project to rival the scale of 69 Love Songs, the staggering, tender-hearted, and wickedly funny Magnetic Fields opus that, upon its release in 1999, earned the synthesizer and ukulele-playing lyricist deserved comparisons to such revered songsmiths as Cole Porter and Stephen Sondheim.  

Until now, that is. On Friday, Magnetic Fields will release 50 Song Memoir (Nonesuch *** 1/2), a grandly ambitious work. On five discs, it tells a version of its author’s life story, with one tune penned to correspond to each of his 50 years. (Merritt turned 52 last month but started work on the album  in 2015 on his 50th birthday.)

So far, the seven-piece Magnetic Fields have performed 50 Song Memoir only twice: At Mass Moca in North Adams, Mass., and at the Brooklyn Academy of Music. They’ll make it three when they kick off a U.S. tour in Philadelphia March 15 and 16 at Union Transfer. In two nights, 25 Memoir songs will be performed in order each evening.

It’ll start with “Wonder Where I’m From,” which conjures Merritt’s conception:  “In St. Thomas, barefoot beatniks bonk on a boat afloat in rum.” And it will close with “Somebody’s Fetish,” a surprisingly sanguine finale from the bass-voiced auteur with a reputation as a droll sourpuss: “And even I, with my wildebeest’s face, my eccentricities, and my freedom from grace / Even for me has Cupid found a place ... at last!”

An autobiography in song was not Merritt’s idea. In 2014, Nonesuch head Robert Hurwitz took Merritt out to lunch at the Grand Central Oyster Bar and pitched the project.

“I wanted to make sure no one else had done it,” Merritt says, talking from his home in New York. “When I saw that no one had, I thought, I better hop on it.” He got worried upon hearing  that Rick Astley was calling his half-century album 50. “Though that only has 12 songs on it, so it’s not really competition.”

Merritt had recently completed a fact-based cycle of songs commissioned by Ira Glass for National Public Radio’s This American Life. “I had just done some documentary songs, so writing 50 more was not as scary as it might have been.”

The radio episode, titled "This Is as Hard for Me As It Is for You," was about a man named Will Ream. “I had to be very careful not to misrepresent him,” says Merritt. “I wanted to make sure that he would not be upset and his children would not be upset. I felt a major responsibility to portray him absolutely fairly.”

In writing about his own life, Merritt felt the same duty in regard to real people he put in the songs. “I played the songs or sent the lyric snippets to the people being portrayed,” he says. He did not feel bound by the same rules regarding himself, though: “With me, I can change my opinions based on what the rhyme scheme demands.”

Navel-gazing is not Merritt’s nature. “I don’t do any probing or soul searching,” he says. “I do not approve of it. 

“Ordinarily, any confession that might be in my lyrics is not pointed to, so you don’t know it’s there. ... I have no interest in the audience knowing who I’m sleeping with. I never understood why musicians” -- he mentions Taylor Swift  -- “would want their audiences to know that.”

Merritt has mostly stuck to the nonconfessional rule, though there have been exceptions. 69 Love Songs’ country-flavored “Papa Was a Rodeo,” makes reference to his father, the songwriter Scott Fagan, who had a brief affair with Merritt's mother, Alix, in the 1960s. The two met for the first time in 2012. Another is “I Thought You Were My Boyfriend,” from the 2004 album i, in which all songs begin with the first-person pronoun.  

His mother provided research assistance by making a timeline of her son’s first 25 years. His manager Claudia Gonson did the second 25.  For conceptual consistency, he intended to play 50 different instruments, but the total ended up closer to 100.  

Merritt chronicles his days in indirect ways.  “Ethan Frome” is about the 1911 Edith Wharton novella he reads every year on his birthday. “They’re Killing Children Over There” takes its title from words uttered by Grace Slick regarding the Vietnam War when his mother took him to see Jefferson Airplane in 1970.

“People who might be dead cannot have their feelings hurt,” Merritt says in relation to “Life Ain’t All Bad,” partly about “my mother’s dreadful boyfriend,” whose ice cream truck he worked on outside Boston when he was 10.

Some years inspired elegantly universal tunes, like “Have You Ever Seen It in the Snow?” about a 2001 winter storm. Others are thornier: “Quotes” responds to the imbroglio when New Yorker critic Sasha Frere-Jones, in 2006, accused him of racist musical taste: “All those ‘quotes' you never said will drown out anything you say / All those trolls who want you dead will dance around your auto-da-fe.”    
In the album notes, Merritt writes: “It’s mostly love and music, so don’t dig for much of a storyline. And if things get mellower as 50 looms, that’s life.”

As the album winds down, he makes room for optimism and a smidgen of sentimentality. The jaunty, “Fetish” embraces a world where “if your forte is brains or appearance / Every persuasion has it’s adherents.” 

The penultimate “I Wish I Had Pictures” is a matter-of-fact declaration: “It certainly would have helped in the creation of this album,” Merritt says. But it’s also a lovely, melodious meditation on memory and loss. 

“Whenever I make a new record, I’m aware I’m making it in relation to 69 Love Songs,” Merritt says. “It always looms.” As an undertaking, 50 Song “was worse actually. That took a year, this took a year and a half,” due to higher production values.

When revisiting his personal history on stage, he’s had no personal revelations. “I’m trying to get through the next line,” he says.    

Merritt is willing to admit, however, that recording an autobiography in song has taught him something about himself.

“Beforehand, I would have said I’m not capable of doing 69 Love Songs over again,” the songwriter says. “Now, I guess I am capable of doing a lot of big stuff over long periods of time.  But I do hope that I never have to do it again -- or at least wait another 17 years.”