ADDIS ABABA, Ethiopia—The sole voice of opposition in Ethiopia’s 547-member national legislature will soon fall silent—the latest in a long line of people who have given up the fight as the government actively mutes dissent while pursuing populist economic expansion.
Since 2010, Girma Seifu Maru has tried to raise his voice against political abuses while 546 fellow legislators consistently support the government.
But in February, the government electoral board replaced the leadership of Mr. Girma’s Unity for Democracy and Justice party with its own people, effectively making him a man without a party and further weakening an enfeebled opposition.
The board said the party violated its own internal bylaws for appointing leaders. Mr. Girma said the government wanted to break the party, as it has so many others, before campaigning for an election in May kicked off last month.
“The ruling party has already completed the election,” said Mr. Girma, who has decided he won’t run again for a seat in the legislature.
Many pro-democracy activists had hoped for an easing of political constraints following the 2012 death of Ethiopia’s strongman prime minister, Meles Zenawi. But while the government under his young technocratic successor, Hailemariam Desalegn, liberalized the economy, it also tightened the political reins in a manner reminiscent of China and Singapore—Asian economies that modernized while suppressing political dissent.
“They still think that you can shut people up and close down anyone who disagrees with you and get away with it,” said Richard Dowden, the director of Britain’s Royal African Society. “And the fact is, they have.”
Like China, Ethiopia has focused on spurring growth as a way of lifting people out of poverty and providing outlets for aspiration to a nascent middle class. The government is building a light rail in the capital, Addis Ababa, along with a giant dam in the northwest and roads across the country. It has opened hospitals and increased the number of teachers in schools. The promise of a better economic future has made it easy to silence critics, said Mr. Dowden.
A government spokesman said actions have been taken against certain politicians or journalists because they have tried to instigate violence. “Some still want to create havoc, to destabilize the system,” said the spokesman, Shemelis Kemal. Replacing the party leadership of the UDJ party was legal, he said, and served to endorse a faction of the party that proved itself more legitimate.
He rejected allegations that Ethiopia has tried to quash dissent, pointing out that the country has 90 opposition parties and that freedom of speech is protected by the constitution.
Yet in the capital, residents are reticent to discuss politics with a reporter. Phone calls are monitored. Websites critical of the government are blocked, including a number of online political publications written by Ethiopians who have emigrated. Those who stay and criticize the government have difficulty finding jobs or winning business contracts, residents say.
Under Prime Minister Hailemariam, Ethiopia’s government increased enforcement of a 2009 law that limited foreign funding for organizations working on human rights or governance issues, according to Human Rights Watch. As a result, many such groups have shut down. In July, the government jailed 10 bloggers and journalists on charges of associating with groups trying to overthrow the government.
Mr. Shemelis said some of those jailed weren’t journalists and none of them were jailed because of anything they published.
Also in July, the government arrested the leaders of three main opposition parties, including Mr. Girma’s UDJ.
Asked why those in the opposition persist amid repression, Mr. Girma says: “If you are in Ethiopia, the question must be the other way: Why are you not in politics?”
Meanwhile, security forces on at least two occasions last year shot live rounds into masses of people protesting plans to expand the footprint of the capital city into areas controlled by other ethnic groups. Several dozen people were killed.
Mr. Shemelis said the officers were responding with “proportional force” to rioters who came at them with grenades, machetes and handguns.
Even as Ethiopia’s gross domestic product grew at a double-digit pace in 2012 and 2013, the country’s democratic character declined. In a ranking by the U.S. human-rights group Freedom House, Ethiopia has fallen from “partly free” in 2010 to “not free” today.
Last year, Ethiopia ranked 32 out of 52 countries surveyed in the Ibrahim Index of African Governance—a modest improvement over 2013 as gains in health, welfare and security offset declines in political freedom and human rights. The index, issued by the Mo Ibrahim Foundation, provides an annual assessment of government on the continent.
The upshot: Ethiopia’s political opposition is barely visible heading into May’s election. Even some opposition parties who have registered—such as the youth-dominated Blue Party—have said they aren’t sure if they are going to put up candidates.
As recently as 2009, Ethiopia’s Parliament had more than 100 opposition lawmakers. But in a 2010 election criticized by the European Union and the U.S. as unfairly influenced by the ruling party, only Mr. Girma—who ran in a district of the capital dominated by the opposition—and an independent candidate won seats. The independent lawmaker subsequently aligned himself with the ruling party, leaving Mr. Girma as the only elected critic of the government.
Mr. Girma held no illusions that he would sway the decisions of the ruling party, but he planned to use his role to voice the anger at government abuse of power that he argues most Ethiopians feel, even if they would never say so publicly.
He said that once, shortly before Mr. Meles’s death, he accused the former prime minister of misusing terrorism laws to arrest political opponents. Mr. Meles dismissed Mr. Girma in front of Parliament as a neoliberal. The chamber erupted in laughter.
Mr. Girma found more support outside the legislature. He became a regular guest on Ethiopian talk shows and a speaker at international symposiums. As for Parliament, he came to hold a dimmer view.
“It was boring,” he says. “You always talk and no one listens.”
Mr. Girma doesn’t socialize with his parliamentary counterparts—in part because he suspects the ruling party doesn’t allow its members to mix with him and because he considers himself more educated than most in the chamber (He has a master’s degree in economics while many in Parliament have only completed high school or a vocational degree). The national Parliament spends its days approving reports and statements by ministers—any debating happens in closed-door meetings before issues reach the legislative chamber.
As the May vote approaches, Ethiopia has received only muted criticism from the West, including the U.S. Some analysts see Washington to maintain a balance between criticism and security interests—the U.S., has a drone base in the country and provides support to local troops who are serving as peacekeepers in the region’s conflicts.
Ethiopia “has been a major partner of the United States not just in counterterrorism but in creating stability in Africa,” said David Shinn, who was U.S. ambassador to Ethiopia in the late 1990s. The U.S., he adds, is “always weighing how hard it can push on the democratization side and the human rights side.”
Sitting in his small office in a shopping complex in Addis Ababa, Mr. Girma said he plans to try to focus more on his outside businesses. He said he played the only political role that was open to him—tokenism—and did what he could with it. “I have tried to play my role properly, and for that I feel good,” he said. “But usually they are in favor of what helps them stay in power. I think their only motive is this one.”
Write to Heidi Vogt at heidi.vogt@wsj.com