In 1846, Hubbard married Gertrude Mercer McCurdy (1827–1909), the daughter of Robert Henry McCurdy, a prominent New York City businessman, and Gertrude Mercer Lee, who was the niece of Theodore Frelinghuysen, a United States Senator and former vice presidential candidate.
 Her brother, Richard Aldrich McCurdy, served as president of Mutual Life Insurance Company of New York.
 Together, they had six children:
Robert Hubbard (1847–1849), who died young.

Gertrude McCurdy Hubbard (1849–1886), who married Maurice Neville Grossmann (1843–1884)
Mabel Gardiner Hubbard (1859–1923), who married Alexander Graham Bell, the son of Alexander Melville Bell, in 1877.

Roberta Wolcott Hubbard (1859–1885), who married Charles James Bell (1858–1929), son of David Charles Bell and a cousin of Alexander Graham Bell, in 1881.

Grace Hubbard (1865–1948), who married her sister Roberta's husband, Charles, in 1887 after Roberta's death during childbirth in 1885.

Marian Hubbard (1867–1869), who also died young.

Gardiner Hubbard's daughter Mabel became deaf at the age of five from scarlet fever.
 She later became a student of Alexander Graham Bell, who taught deaf children, and they eventually married.

Hubbard's house on Brattle Street in Cambridge (on whose lawn, in 1877, Hubbard's daughter Mabel married Alexander Graham Bell) no longer stands.
But a large beech tree from its garden still (in 2011) remains.
To service his then-modern Cambridge house, Hubbard wanted gas lights, the then-new form of illumination.
So he founded the Cambridge Gas Company, now part of NSTAR.
 After he moved to Washington, D.C. from Cambridge in 1873, Hubbard subdivided his large Cambridge estate.
On Hubbard Park Road and Mercer Circle (Mercer was his wife's maiden name), he built large houses designed for Harvard faculty.
On nearby Foster Street, he built smaller houses, still with modern amenities, for "the better class of mechanic."
This neighborhood west of Harvard Square in Cambridge is now both popular and expensive.

He died on December 11, 1897 at Twin Oaks, his suburban residence.
 His funeral was held at the Church of the Covenant in Washington, where he was president of the board of trustees.
 His widow died during a car accident on October 20, 1909 in Washington, D.C.
In 1846, Hubbard married Gertrude Mercer McCurdy (1827–1909), the daughter of Robert Henry McCurdy, a prominent New York City businessman, and Gertrude Mercer Lee, who was the niece of Theodore Frelinghuysen, a United States Senator and former vice presidential candidate.  Her brother, Richard Aldrich McCurdy, served as president of Mutual Life Insurance Company of New York.  Together, they had six children:
Robert Hubbard (1847–1849), who died young.
Gertrude McCurdy Hubbard (1849–1886), who married Maurice Neville Grossmann (1843–1884)
Mabel Gardiner Hubbard (1859–1923), who married Alexander Graham Bell, the son of Alexander Melville Bell, in 1877.
Roberta Wolcott Hubbard (1859–1885), who married Charles James Bell (1858–1929), son of David Charles Bell and a cousin of Alexander Graham Bell, in 1881.
Grace Hubbard (1865–1948), who married her sister Roberta's husband, Charles, in 1887 after Roberta's death during childbirth in 1885.
Marian Hubbard (1867–1869), who also died young.
Gardiner Hubbard's daughter Mabel became deaf at the age of five from scarlet fever.  She later became a student of Alexander Graham Bell, who taught deaf children, and they eventually married.
Hubbard's house on Brattle Street in Cambridge (on whose lawn, in 1877, Hubbard's daughter Mabel married Alexander Graham Bell) no longer stands. But a large beech tree from its garden still (in 2011) remains. To service his then-modern Cambridge house, Hubbard wanted gas lights, the then-new form of illumination. So he founded the Cambridge Gas Company, now part of NSTAR.  After he moved to Washington, D.C. from Cambridge in 1873, Hubbard subdivided his large Cambridge estate. On Hubbard Park Road and Mercer Circle (Mercer was his wife's maiden name), he built large houses designed for Harvard faculty. On nearby Foster Street, he built smaller houses, still with modern amenities, for "the better class of mechanic." This neighborhood west of Harvard Square in Cambridge is now both popular and expensive.
He died on December 11, 1897 at Twin Oaks, his suburban residence.  His funeral was held at the Church of the Covenant in Washington, where he was president of the board of trustees.  His widow died during a car accident on October 20, 1909 in Washington, D.C.
Gardiner Greene Hubbard