Lowell native Brendan Fleming bucked the urban renewal juggernaut sweeping the nation in the 1960s and urged his hometown to preserve the boarding houses and factories where America’s historic Industrial Revolution hit its peak.

But city leaders came close to telling Mr. Fleming to jump into the Merrimack River. The City Council in 1966 rejected his call for creation of a historic commission, and Mr. Fleming was not reappointed to the Lowell Redevelopment Authority.

“I was told that the history of Lowell best be forgotten,’’ Mr. Fleming said in a 1994 interview recorded for the University of Massachusetts Lowell’s Center for Lowell History.

“I’ll never forget that statement being made. And I thought it was just so lacking in knowledge of the history of Lowell,’’ Mr. Fleming said. “I said at that particular point in time that I was going to try to do something about it.’’

With a low-key style and a reputation for meticulously studying the issues, Mr. Fleming eventually triumphed. He was elected to the City Council in 1969, and kept his seat for the next 23 years.

Mr. Fleming, who was a math professor at UMass Lowell and its predecessor, Lowell Technical Institute, for 40 years, died May 28 at Bridges by Epoch, an assisted-living facility in Westford. He was 90, and his health had declined.

He served as the city’s 75th mayor from 1982 through 1984, a largely ceremonial position in Lowell’s city manager form of government.

He helped win creation of the Lowell Historic District Commission in 1971 and establishment of the Lowell Locks and Canals Historic District and the City Hall Historic District. Lowell National Historic Park was then established in 1978.

“He was a pioneer for preservation in Lowell, who had the vision to see what was valuable,’’ said Paul Marion, a UMass Lowell professor and author of “Mill Power: the Origin and Impact of Lowell National Park.’’

“His confidence in Lowell’s heritage was borne out by not only the national park but the whole cultural renaissance in the city that put it on the map as an important American place, reclaiming its status from the 19th century, when it was the model factory city,’’ Marion said.

There was one part of Lowell’s history, though, that Mr. Fleming did not care to celebrate. In 1986 before a packed room, he was the only member of the City Council who voted against creating a park in honor of novelist Jack Kerouac, an icon of the Beat Generation, who was born in Lowell in 1922 and died from the effects of alcoholism at age 47.

“I just voted from my gut,’’ Mr. Fleming later told the Globe Magazine. “I voted the way I did because I just didn’t feel Jack Kerouac’s lifestyle is the kind of lifestyle you should memorialize.’’

Lowell’s children could learn a better example from a park named in honor of its other famous citizens, he said, such as General Hoyt Sanford Vandenberg, a World War II Air Force commander, or actress Bette Davis.

Though both were born in Lowell and into devout Catholic families, Mr. Fleming’s philosophy of life couldn’t have been more different than Kerouac’s. The math professor believed in God, family, and country, his family and friends said.

Born Martin Brendan Fleming on Feb. 2, 1926, Mr. Fleming’s parents, Martin and Anna (O’Malley), emigrated from Ireland as teenagers. He was their second son.

He grew up amid the tight-knit congregation of Sacred Heart Church, which closed in 2004, and graduated from Keith Academy in the class of 1943.

The only time he ever lived away from Lowell for long was during World War II, when he served in the Navy in the Pacific.

As the military prepared to invade Japan in those years before Japan’s surrender, Mr. Fleming was a quartermaster aboard the USS LCI-714.

After the war, he earned undergraduate and master’s degrees in mathematics from Boston College.

Friends introduced him to Bernice (Kenney). They were married for 55 years and had seven children. She died in 2007.

“He was such a good father. I like to joke that I was home-schooled because he was always teaching through example,’’ said one of his sons, Thomas, who was a member of the Lowell Police Department for more than 30 years.

He recalled how he and his siblings campaigned for their dad, leaving leaflets at homes across the neighborhood and holding signs on Election Day.

The city manager usually came to the family home on Friday afternoons to quiz Mr. Fleming on how he was going to vote at the council meeting come Tuesday night, Thomas recalled. “He knew dad wouldn’t change his vote,’’ he said.

Mr. Fleming sometimes combined family time with his council business. While schooling himself on issues surrounding solid waste disposal, Mr. Fleming once took his children to Rhode Island on a trip to view an incinerator.

Thomas said he now marvels at how his father managed to juggle his college teaching career with his City Council work, all while making lots of time for his children.

His father and mother were “inseparable,’’ Thomas said. Leaders who invited Mr. Fleming to events in Lowell always made a place for Mrs. Fleming, too, he added.

In addition to Thomas, of Chelmsford, Mr. Fleming leaves three daughters, Marybeth Holak of Windham, N.H., Ann Marie Crafts of Chelmsford, and Patricia Quigley of Quincy; three other sons, Martin of Greenwich, Conn., James of Wheeling, W. Va.; and Edward of Arlington, Va.; 14 grandchildren; and seven great-grandchildren.

A funeral Mass was said in Immaculate Conception Church in Lowell. Burial was in St. Patrick Cemetery in Lowell.

Mr. Fleming served on many boards and committees during his life, including the Massachusetts Police Association, several Catholic organizations and schools, and on the board of St. John’s Hospital in Lowell.

He retired from UMass Lowell in 1996. Earlier this year, the college announced an endowed scholarship in his name for math majors, with special preference for students who are from Lowell.

Maura Doherty, a Lowell native and historian who authored “Canaries in the Coal Mine: The Deindustrialization of New England and the Rise of the Global Economy,’’ recalled how Mr. Fleming helped her find resources for her dissertation on Lowell, titled, “Spindle City Blues.’’

“He brought professionalism and grace to the City Council and to the office of the mayor. He was kind and compassionate, especially to those with which he disagreed, and always seemed to keep things light,’’ said Doherty, who now teaches in Switzerland.

“Brendan never tooted his own horn, and that is why current histories overlook the crucial role he played in Lowell’s revitalization. He helped to form consensus and move the city forward economically and in historic preservation and reuse,’’ she said.