Charles Carroll Glover found a new and powerful ally in Sen. John Sherman of Ohio, whom he called upon with a new draft bill supported by his lobbying group. On December 4, 1889, at the start of the 51st Congress, Sherman introduced the bill. Senator Ingalls resubmitted his own bill but deferred to Sherman's version, which the District committee swiftly reported and brought to the floor. The Senate amended its provisions for financing and management, passed the bill on January 28, 1890, and sent it on to the House. 
On March 18 the House District committee, now chaired by Rep. William W. Grout of Vermont, recommended House approval of the bill with further amendments. One, inspired by the forthcoming quadricentennial of Columbus's discovery of America, would designate the area "Columbus Memorial Park." Another would have the District of Columbia pay half the park's cost from its revenues. Bringing the bill to the floor a week later, Grout minimized development prospects. He foresaw initial action only to enclose the grounds and to erect over the entrance an arch, whose cornerstone would be laid on the 400th anniversary of Columbus's sailing. "Let future generations, and as opportunities arise, develop this park into a thing of beauty, when there will be a million of souls here, at the end of the next century," he declared. 
Opponents were not mollified by the cost-sharing provision and the talk of deferred development. "Mr. Chairman, this city of Washington is growing to be a very expensive necessity to the people of the United States," complained Rep. Daniel Kerr of Iowa. "We are beginning to think, out West, that if the people here want breathing-places they should provide them by taxing themselves, just as Chicago, St. Louis, and other places have done." After lengthy debate, further consideration was postponed until April 28, when Representative Payson introduced and the House adopted a lengthy amendment designed to make benefited adjoining land-owners defray park costs. Even so, the bill was then defeated by a 78-88 vote. Supporters marshaled their forces and brought the measure up again a month later when it passed 107 to 82. 
A conference committee was needed to reconcile the different House and Senate versions. The resulting compromise restored the Senate's "Rock Creek Park" designation but in most respects favored the House, whose provisions for assessing neighboring landowners and cost sharing were retained. Senator Ingalls called the latter "an unjust burden upon the already overtaxed resources" of District residents, but as a conferee he supported the committee's product. Both houses approved it on September 25, 1890, and President Benjamin Harrison signed the legislation into law two days later. 
The Rock Creek Park authorization came at a significant time in the development of what would later become the National Park System. In 1872 Congress had reserved the first area titled a national park, Yellowstone, "as a public park or pleasuring-ground for the benefit and enjoyment of the people"; its authorizing legislation went on to prescribe regulations to "provide for the preservation, from injury or spoliation, of all timber, mineral deposits, natural curiosities, or wonders within said park" and their retention in their natural condition." Not until September 25, 1890--the day Congress completed action on the Rock Creek Park bill--was another permanent national park, Sequoia, authorized. A vast natural wilderness area, Sequoia's kinship with Yellowstone was clear. But the legislation for Rock Creek Park as well as that for Sequoia adopted language from the Yellowstone act. Each was "dedicated and set apart as a a public park or pleasure ground for the benefit and enjoyment of the people." The protective prescription for Rock Creek, modified slightly from that of the other two areas, called for regulations to "provide for the preservation from injury or spoliation of all timber, animals, or curiosities within said park, and their retention in their natural condition, as nearly as possible." 
Enactment of the Rock Creek Park bill was followed four days later by authorization of two more national parks: General Grant (predecessor of Kings Canyon) and Yosemite. Thus, although not on the scale of these California wilderness preserves and lacking their "national" park labels, Rock Creek Park was part of the first post-Yellowstone influx of natural parks established by the federal government. 
The Rock Creek Park act provided for acquisition of no more than 2,000 acres extending north from Klingle Ford Bridge, the northern limit of the National Zoo. It created a commission comprising the chief of engineers of the Army, the engineer commissioner of the District of Columbia, and three presidential appointees to select the land and have it surveyed by the assistant to the engineer commissioner in charge of public highways, who would act as executive officer. Recording of the survey map would constitute condemnation of the included properties. A procedure was prescribed for compensation, requiring the supreme court of the District to appoint another commission to appraise the values of lands whose owners did not accept the prices offered; this valuation when approved by the President would be final. Having ascertained the costs of the lands and related expenses, the park commission was to "assess such proportion of such cost and expenses upon the lands...specially benefitted by reason of the location and improvement of said park, as nearly as may be, in proportion to the benefits resulting to such real estate."
The act appropriated $1,200,000 for all survey, appraisal, acquisition, and related costs, half of which would be reimbursed to the Treasury from District revenues. Likewise, half of the annual appropriations for park improvements and maintenance was to be charged to the District. When established, the park would be jointly controlled by the District's commissioners and the Army's chief of engineers, "whose duty it shall be, as soon as practicable, to lay out and prepare roadways and bridle paths, to be used for driving and for horseback riding, respectively, and footways for pedestrians; and...to make and publish such regulations as they deem necessary or proper for the care and management of the same." 
The long legislative battle had been won. But Rock Creek Park existed only on paper. Still more time and toil would be needed to make it a reality.