CITY HALL — Terry O’Day, an environmental activist who helped lead a campaign to defeat an anti-development measure last fall, resigned from the Planning Commission on Thursday citing a need to focus more attention on his family and career.

The one-time City Council candidate and married father of two young children submitted his resignation letter to Eileen Fogarty, the director of planning and community development, who is out on vacation this week. The commission’s previously scheduled meeting on Wednesday was also canceled.

“I just need to make some space for other areas of my life where I’m needed, both personal and professional,” O’Day said during an interview on Friday. “I need to dedicate myself where I’m needed.”

O’Day, who is the executive director of locally-based nonprofit Environment Now, was appointed to the Planning Commission in 2003 and was its chairman in the past year, serving during a time when the quasi-judicial body was often busy with matters related to the Land Use and Circulation Element, the 20-year-update to the city’s general plan.

“I loved thinking about how our community works and how I can make it better,” he said.

The commission has changed since the time when O’Day was appointed, including improving its relationship with the Planning and Community Development Department, one that he called “terrible” in the early years.

He said that the commission is in a strong position where he feels comfortable leaving.

“I know there are good folks in the wings that are ready to fill in for me,” he said. “The commission is really strong and capable and working really well together.”

In addition to the Planning Commission, O’Day last year co-chaired the Save Our City campaign, which came out against a ballot measure that would have limited commercial growth to 75,000-square-feet a year. O’Day said at the time that the measure would have serious consequences for sustainability initiatives by impacting adaptive reuse, mixed-use projects and the ability to create transit-oriented communities. Proponents of the measures said that limits needed to be set to better control commercial growth and the traffic that comes as a result.

O’Day ran for the City Council in 2006 and made a strong showing despite finishing fourth, coming just behind incumbent Bob Holbrook with 16 percent of the vote. He was among more than 20 candidates who submitted their names for consideration to replace the late Councilman Herb Katz after he died in January. Gleam Davis, his colleague on the Planning Commission, was eventually appointed.

Fellow commissioners praised O’Day for bringing a unique environmental perspective to the table, along with strong management skills from his background overseeing a nonprofit organization, which came in handy when he took over as chair.

“I think the combination of those really allowed us to focus more clearly on what it is that we were trying to do,” said Gwynne Pugh, who joined the commission about six months after O’Day.

Hank Koning, the vice chair of the commission, said that O’Day brought a balanced outlook on land-use issues and made sure to come in without an opinion already formulated.

“He was a fabulous chair and fabulous commissioner and it’s a bummer that he’s leaving but he’s got to do what he’s got to do,” Koning said.